<<<Current build is 2x perception 2x ranged and 1x ambush. Since sniping takes perception and ranged into account vs. open aiming which only use perception ranks am I losing 25% of my aiming ability when shooting from hiding? >>>

I assume you meant perception and ambush for aiming from hiding. But my ranger's skills are exactly like yours, and I don't notice much difference between open aiming and hiding. If anything, I think hiding might be a smidgen more accurate, but it's hard to tell. My feeling is that this is the baseline training (2x ranged, 2x perception, 1x ambush) for a sniper. This is based solely on my own training and observations. In any case, I'd guess I'm able to hit the eye about 85% of the time, if not more.

~ Heathyr and friends