An awareness test works based on the sense giving aware the target. Different situations would give bonuses or penalties based upon many factors and what sense is being used. This is the reason there are GMs for games like this.
A Tau stealth suit in passive mode forces a significant number of penalties for sight based awareness tests, but NONE for hearing. On the other hand, a stealth suit using silent movement could still only be heard at a fairly close range (which for space marines isn't what we mere mortals would consider close) due to the care and low volume of its movement. If it were running full tilt over uneven ground, then it would be much easier to hear at longer distances (and be easily seen as the suit is no longer trying to hide its movement with the hide skill, though any situation providing natural obstruction like smoke etc. would benefit from passive visual penalties).
Put it another way: Someone stolling down the road whistling a tune could easily be seen from 2 miles away (especially by space marines), but the person's whistling couldn't be heard. Now imagine the guy is walking down the street and you are around a corner of a building from him. You cannot see him, but since he's only a few score feet away you can hear his whistling.
Right, those examples are somewhat different from what happened in my game, and they make perfect sense. So, let me give you some context.
My team enters a training arena and all seems fine. However, as the GM I know there is more at stake. To speed the process up I rolled Awareness tests for all of their characters as it is obvious a group of Marines inserted into a hot combat zone would be scanning for adversaries. Now, I did one test for each character. Two characters passed the test - one with 1 DoS and the other with 2 DoS. I sent private messages to each of them.
For the 1 DoS, he gleaned info about an objective based on sight. The 2 DoS got the same sight info, but also heard something farther away. Is this OK for this particular situation?
However, in a skill check that is about to happen, my assault marine is going to jump 30m into the air to scan his surroundings. I was going to roll once for sight, once for hearing, and once for smell (SW) - since his sight is going to be greatly increased because of the jump, im going to give him a situational +30, but since the jump pack is so loud, his hearing test will be at +0, while his smell without a helmet will be at +10.
Am I overthinking and over complicating this to all Hell? Haha. Thanks for the patience.