The usual math for skills and other factors applied to abilities is
<base value> x ( 1 + (<skill bonus> / 100) )
Some abilities don't use the full value (i.e. may only use 1/2 of the skill bonus) for balance purposes. And there isn't a full know list of which abilities which don't follow it. One set that has been acknoledge are hold and stun skills)
The sensors captain skill, as well as relative consoles, only affect the stealth detection aspect of Sensor Scan. They also have a secondary affect increasing resistance to certain powers like scramble sensors. The debuff is entirely dependant on Aux power level now, which I am not happy about because before the new skill tree my SS was debuffing much more than it does now.
Auxiliary power doesn't utilize the same power usual power curve (25 : B x 1/2, 50 : B x 1, 75 : B x 3, 100 : B x 4, 125 : B x 5). Auxiliary Systems power curve is much flatter. (From memory) Aux 75 is base value. B x 1. Aux 25 is 1/3 less B / 1.5. and Aux 125 is 120% of base.