Just a quick and simple question: How many hits are used AFTER breaking through a masked aura?
All hits or just the net hits?

Or is it a two tests mechanism, one for opposite test and one regular Assessing test?

In an opposed test, the character generating the greater number of hits achieves their goal. The assensing magician is trying to scan the aura (which, probably unknown to them, is masked), while the masking magician is trying to present false information. It's still an Assensing test for all purposes, so the number of hits the assensing character rolls should still indicate the amount of information they receive from the aura - the opposed test just determines whether that information is accurate or not.

So: one Opposed Test, all your hits apply to the Assensing Table.

So wouldn't that be two separate Success Tests, one by each party, instead of a TRUE Opposed Test? Or am I confused as well?

Example time!

Hexslinger Holmes is trying to assense the aura of Snowblood for signs of her making a pact with a Shadow spirit he's been hunting. Holmes has Intuition 3 and Assensing 4 (Aura Reading +2); Snowblood has Magic 3, Intuition 3, is a Grade 1 initiate, and has a Force 1 power focus.

Holmes rolls (Assensing + Intuition) 9 dice against Snowblood's (Magic + Intuition + Initiate Grade) 8 dice. If Holmes scores three hits and Snowblood only 2, then he sees through Snowblood's masking and gets all the information revealed by 3 hits on the Assensing Table (and knows that she was masking her aura). If Snowblood scored 3 hits and Holmes 2, then he would receive the 2 hits worth of Assensing information - but about the false aura! If the two tie, then Holmes does not pierce the masking and gets no information (or the GM can go "response hazy, try again").

Hmm, why is this the only occasion, where the result of an opposed test is a function of the gross hits of the winning player instead of being tied to the net hits?

Net Hits are the number of hits that exceed a given threshold. Thresholds are never applied to Opposed Tests. You don't have Net Hits for an Opposed Test, you just have the hits you score and the hits your opponent scores. Assensing Tests in general do not have a threshold, and so Net Hits don't apply to them.

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This is not directly outlined in the book, but from a gamemaster perspective this is very beneficial. The player can roll their dice in plain view, and the GM can secretly roll the opponent's dice behind the screen. The player will know how much information they gain from the hits they score - they just don't know if it's the actual information or if the target is masking, unless they beat the masking and the GM tells them they see the false aura as well.

This is how we have always used it and it works great for us...

At least in combat the net not gross hits have always been the important factor, the same goes for direct combat spells, and all other resisted i.e opposed spells.. The examples for social skill tests on p. 131 of SR4A also use the net hits as relevant criterion.

Net hits is also used (mostly informally) to refer to the number of hits that exceed your opponents hits in an Opposed Test; a term used as a measure of how much one exceeds the other, and in this (informal) case it does sometimes see used in Opposed Tests - notably, as you said, in combat. Still, this is an exception to the general rules of Opposed Tests, and are usually specific to certain skills and tests.

It doesn't apply in attempting to pierce Masking (or many other Opposed Tests) because it's an all-or-nothing deal - Masking doesn't reduce the information a character can get from Assensing, it just provides false information.

This type of system means that PCs (and therefore NPCs as well) never get that, "Hmm, they are just normal people. Normal people whose aura is oddly difficult to get information off of. I call shenanigans!"

Huh.

It makes perfect sense, AH! Thanks!

Caadium, an excellent point! Anything that allows me to mislead the players in RAW opens up all kinds of shenanigans behind the scenes!

Of late, I have been struggling with overly perceptive characters, who have made me do quite a bit of tap-dancing to keep the plot line hidden long enough. Fortunately, my mage player's character has a VERY low Assensing skill, and is usually oblivious, to the point she ignores astral most of the time, which leaves me a free hand to use astral space to screw them all over! MUHAHAHAHAHAHA (cough-cough)!!!

One thing I am trying to do is avoid metagamey hints from dice rolls and modifiers, and this Assensing "Opposed" Test and Gross Hits (not Net Hits) means the player will not really know if it was true or false from his own roll.

I wish I had the same kind of thing for some of the regular Perception Tests. Some of my players get 5+ Successes on a Perception roll with all their cyberyes/ears etc. and it doesn't always make sense that there is an opposing roll on my part.

I see no reason why this same mechanic couldn't be used for other opposed perception checks. For example, something is hidden and they make their check. They get 5 hits on the perception check, but how many did you get on the hide roll? If you got 6, you can describe how thoroughly they searched only to find nothing. The same hold true for disguises, or really any other type of opposed perception. The key is to make sure you get into the habit of rolling and checking dice each time. Many players will call shenanigans if you only roll sometimes and they don't find things on those instances.

Also bear in mind that not all sensory input is helpful in all situations. In fact, there is such a thing as sensory overload. Its entirely possible to have different elements limiting different senses as well. Don't forget, that someone putting that much effort into checking something out is fairly focused. While they are 'checking the door for traps' they could very easily fail to notice the hidden gun port open up on the other side of the room (yes, this is a joke example and a parody ... sue me).

So if you skillfully try to hide something from a skilled searcher, the searcher finds more stuff than if a klutz tries to hide something from a nearly blind person? That's weird IMHO. Example:

Person A tries to hide something with 5 hits and Person B gets 6 hits for the search, so he is only marginally better than A. But the GM is supposed to judge according to the 6 hits what he finds?

However if Person C has no success at hiding his stuff and person D is also only marginally better at finding it with 1 hit. He is supposed tp find significantly less stuff? I don't get it.

Wait...why is that strange?

Two baddies hide their commlinks in a room:

The klutz hides his comlink by sticking it in the drawer - which is the first place either searcher would look, so they find it no problem...but the skilled searcher would also find a card from the guy's favorite nightclub, a forgotten credstick in the mug-o-pens and some other stuff before finally finding the good hider's commlink in a hidden panel in the baseboard.

That really works quite well, actually.

If there are other things that the searcher did not look for this may be an option.

Now let's look at an opposed test where adding non related bonusses like that is not possible: One person tries to keep a door shut while the other tries to push it open.
If two weaklings are doing it and get 0 and 1 hit respectively, according to your interpretation the door opens a lot more slowly than when two trolls do the same thing and get 5 and 6 hits respectively. the net force however should be the same.

Hmm...in that particular case, I'd say the doors open with the same speed, but the one which the trolls are wrestling over is a lot more beat up - ripped off the hinges, perhaps.