I don't have a problem with full armour on cyber-hands/lower arms. Feet seems a little nonsensical but then with lower capacity comes lower armour, swings and roundabouts. You can only make the system so accurate before you end up playing Rolemaster.
In particular Hands and Lower Arms really ought to give disproportionately large armour values. These are the areas where the vast majority of defensive wounds are seen because these are the areas we instinctively use to defend ourselves from attack.
In particular Hands and Lower Arms really ought to give disproportionately large armour values. These are the areas where the vast majority of defensive wounds are seen because these are the areas we instinctively use to defend ourselves from attack.
It is precisely cyber-hands and lower arms that give me pause about the armor being cumulative rather than an average.
This is how I see armor working in Shadowrun. Since there aren't actual hit locations, one must assume that in Shadowrun strikes hit the body in a random scatter. The higher the armor value the less likely you are to hit an unarmored or less armored location.
To pull some BS numbers... armored vests are 6/4, I mentally picture these to cover most of the torso. Now 6/4 is good enough to put most weapons, outside of assault rifles and higher classed weapons (in general), into the stun track without net hits. In reality, because of the % of mass that your torso takes up, this if where you're most likely to be shot. Yes I know, this means that technically for a pistol to wound someone with an armored vest it means they're hitting an arm or a leg....
This is what leads people to interpret armor stacking from cyberlimbs.
When using this interpretation with regard to partial cyberlimbs. I just fail to see how a cyberhand can provide as much of an armor benefit as a lower cyberarm, or a full arm cyberlimb. Likewise I fail to see how a cyberfoot can grant the same amount of armor as a full cyberleg. Granted I can only get 2 armor out of a cyberhand or cyberfoot. This silliness exists regardless of if you average or stack it, but it is -less- silly with the average compared to full value due to the amount. Four full cyberlimbs would get you 16 armor, while the hands and feet get you 8. So replacing what I estimate is about 15% of your limbs with cyber lets you get 50% of the armor that you would have gotten if you did full replacements. If you average you get 1 armor from the hands and feet, and 3 armor from the full replacements. 15% replacement for 33% of the armor.
Instinct guarding, resulting in lower arm and hands taking more hits, only works when you can see the attack coming. It's a reflexive action. You're more likely to use it in melee combat, but if someone takes some pot shots at you with a suppressed or silenced firearm, you aren't going to do this. As such, using the "likelyhood to block with lower arm" as a reason to justify same arm values on partial limbs is essentially grasping at straws. If you can't apply it equally, don't both to apply it.
Now, here's some other reasons I support averaging the armor values.
#1 - Balance. So you built a character that has the max possible armor on cyberparts (post creation). You have 22/22 armor from your cyberlimbs and your sporting heavy military armor with a milspec helmet that gives you an additional 18/16 for a grand total of 40/38. You're basically immune to small arms fire. However if you're this character, that means that as a GM I have to up the challenge, standard guards don't work anymore, they're like flies to you. That means I'm upping the gamut. I'm going to be throwing tanks, rockets, missiles, grenades, and assault cannons at you since there are the only things that will start to have damage values or armor penetration to make them effective, and the NPCs are going to start getting higher skills levels in those various weapons. They're also going to be far more armored as well so that they have time to stand up to you. Fine and dandy, you can take it. The rest of your team may not be so lucky and are more likely to turn into a red mist, and may be utterly ineffective at defeating the enemy.
This is power creep. I absolutely hate it. I loath it. I despise it. I all of that towards it because it forces the GM to up the difficulty for the power creeper, which hurts the rest of the players, or have the GM keep everything the same in concern of the other players, in which case the power creep is over powered and everything is a cake walk. Or the players have to do the same types of bullshit to keep up with the power creep. These are the few situations where I, as a GM, are likely to rule zero you on that. Even if its totally legit to stack each individual cyberlimb armor with no encumbrance factors, I'll still rule zero it because I won't subject my players to power creep. I'll kill it before it can even be a problem.
I saw the exact same thing when I played Rifts. We had a Glitterboy, the rest of use were itty bitty people compared to it. The Glitterboy destroyed everything, and the GM upped the difficulty on everything because of the Glitterboy. It made the rest of us fairly ineffective against what we were fighting. This continued to cascade until such a time that I said fuck it, my weaponry was ineffective, that I just chucked a grenade into the middle of a melee involving my party and the enemy. That was the first time I recall doing damage to my enemies.
#2 - I've seen nothing to suggest to me that 3 armor on a cyber limb is any more potent than Rating 3 Dermal plating or Orthoskin.