I'm grasping it a little better. I get what I want when I set it to auto. The problem I was having was with the games with starfields (one other I believe). I don't have any filtering on. I'm trying to figure out how that Galaxian snap represents what's on screen. Why does it look so different when playing?
I know MAME is all about accuracy but it would be nice to have an option to take a snap as it is displayed while playing. At least for frontend use. No matter how I configure the snap dimensions I get a fuzzy picture of Galaxian (and others). It's only very slight but it prevents a perfect sprite rip. I'm must be missing something but I'm not sure how a squished snap is useful.