Whenever I use UPP or KSG (on silver) I try to apply it so thin that I can't see it. To ensure adequate coverage I work very methodically and somewhat slowly. It takes *far* less product than you'd imagine to provide full coverage and protection. Six layers of KSG applied this way last me well over a year on a daily driver (still beading, just starting to sheet, you can still easily feel the KSG on the surface). I reapply my UPP whenever it starts to lose slickness, but I still get plenty of protection from very thin layers of that product also.
I go by feel when applying. The areas you've covered will be slicker than those you haven't. When buffing it off, I fog the surface with my breath. The condensation shows the product and also makes removal a bit easier. The small amount of water vapor has never, in my experience, compromised my sealants in any way.