Ya know, I don't see a -2 Target Concealed modifier, either. I think I was holding that over from either a previous edition, or a different game. All previous comments regarding that mod on my part are invalid.
The problem that a lot of players and a lot of groups have in Shadowrun is that they don't *get* into firefights, they get into gunfights. I break these up along two really rough lines:
Gunfights are when you shoot at someone who's shooting at you.
Firefights are when you shoot in the direction of someone who's shooting at you.
If your team kicks in a door, and you start trading rounds with the couple of guys in that room, you're in a gunfight. If one of the yahoos in your team decides to suppress the room for some reason, that doesn't make it a firefight... it just means he likes to waste ammo, or he's worried about something invisible/behind the sofa, or whatever. They usually happen at distances of a few meters, and they're usually over in a few seconds, because everyone's done shooting, been shot, or both. Your objective is "survive for the next couple of seconds" with the occasional "escape" or "kill" added on.
If your team starts taking fire from a building across the street, and they start returning fire at shadows and muzzle flashes in the building, that's a firefight. You don't, in fact, have a precise idea of where your target is. Your objective can be a lot more complex, since you've got more than a couple of seconds to complete it.
Someone said earlier that if you're going to take a Simple Action to OiD before each shot, you aren't going to be getting much done. At the kind of ranges that a gunfight happens, that's somewhat valid... when a troll is running at you with something sharp from a few feet away, you don't belong Observing in Detail to check how he's armored or what kind of weapon that is in his hands, you belong spending your SA's putting rounds into the guy because you've only got enough time to get off a couple of shots before he sticks you. Of course, if you blew your Perception roll when he showed up, he might turn out to be the scientist you're supposed to meet to steal the prototype nanosword, but hey, them's the breaks. Normally, this would be Obvious, and wouldn't require a Perception check at all, but if you're involved in a gunfight and a troll with a sword shows up, target ID is kind of critical.
Shadowrun doesn't do
firefights very well, and they take forever if your goal in the firefight is to flatline everyone on the opposite side. When the bullets start flying, it becomes obvious to everyone within a few seconds that they are, in fact, under fire. People who make their Surprise checks can get their heads down real fast. People who don't make their Surprise checks lose that first IP, but can get their heads down within a few seconds of the gunfire starting (essentially, the difference between "OH, CRAP!" and "Why the heck is that windshield shattering... OH, CRAP!").
Beyond that point, it's a matter of figuring out what's going on. Where's the fire coming from? The situation is hectic... penalty there. You're specifically looking for the gunfire (as opposed to "You notice a red-breasted woodpecker on the power line above the street")... bonus there. Gunfire is frequently loud and obvious... bonus there. It is not
instantly obvious down to what floor of the building and what side of which window shooters are operating from. If it were, people wouldn't ever get pinned down, because the moment they took fire they'd be able to effectively return it. Once you've nailed it down to an approximate area, suppressive fire is a possibility, just to get lead going in the right direction, and reduce the amount of suppression your own troops are dealing with so that they can effectively return fire. Plus, you shooting in the right direction gives people around you who might not have figured it out yet some pointers.
If you're continually blowing the Perception check, it's not that you don't know you're being shot at, it's just that you don't know from where. Maybe every time you peek up to look around, bullets hit your cover and you duck back under. Maybe you're trying to eyeball your attackers, your ammo readout, and yell into your comms at the same time and it's just too much to handle. Maybe you got distracted by the strobe light from the rave across the street and it took you a second to figure out "that's not muzzle flash." Whatever, you blew the roll, and didn't get the information you were seeking.
Once you manage to nail down a little more specifically where someone is (for example, you manage to spot him leaning around from the right side of the windowframe, rather than just looking for the big flashes), you can start engaging in actual targeted fire. If he ducks back, you're going to be making blind fire shots, but it's worth a try. If he ducks back and moves to another location
, you're still going to be making blind fire shots... but your GM isn't going to be bothering to see if the bullets do much more than poke holes in the walls, since there's no target where you're blind firing.
If the yahoo is inexperienced enough or high enough to be standing in the window and shooting down at you repeatedly, picking him out and hitting him isn't going to be hard, as far as these things go. The guy he's firing at stays behind his cover, and one of his teammates returns aimed fire. This is one of the reasons that military units going up against disorganized civilian shooters tend to significantly outperform them... really basic things like "don't keep shooting out of the same window all day" can
be learned through trial and error, but "error" usually involves getting shot.
Prepared or skilled shooters will do what they can to avoid being exposed to anything more dangerous than suppressive fire. Blind fire can still kill you if you're unlucky, and aimed fire usually means you're about to feel the pain. This is why ambushes, suppressed weapons, relocating where you're shooting from, and little tricks like not sticking your gun barrel out the window (and keeping the flash inside the room instead of outside the window, where it's a lot easier to find) help out a lot in a firefight... the enemy only has a vague clue of where you are, and so they're not really able to engage you.
Shadowrun's combat system is really horribly clunky for doing this kind of engagement, and the incredibly precise levels of detail to which any given fraction of a second can be tracked in a SR gunfight have resulted in twitch-ninja encounters where 20+ combatants can go from hidden ambush to total wipeout faster than you can read this run-on sentence. The system is okay for a gunfight, but lousy for a firefight. The disparity in IP's (one-IP characters may find themselves waiting a long, long time for their next opportunity to contribute to the action) exacerbates this problem... people are more interested in getting shots on target than they are in keeping bullets out of their hide.
The critter power Concealment is essentially an extension of things like suppressing your weapon, wearing appropriate camo, crouching on a rooftop half a block away, or coming at the target from behind a bright light source... it makes it harder for the guy to figure out where, exactly, his opponent is and what he's doing. The applications of this in a firefight are obvious... it makes it harder for the people under fire to get any more effective than suppressive fire. In a gunfight, it can buy you those critical couple of IPs before your targets know what's going on (during which you shred them). If a Concealed shooter keeps giving indications that he's there (like shooting at you), then he's going to be getting Perception tests made against him on a regular basis, but you're not going to have anything better than the kind of data you need for Suppressive fire until you nail down some successes.