I feed my BP in his tank. I don't use a lose substrate for him. He eats great. I feed my Kenyan Sand Boa in a deli cup because he's on crushed walnut shells for a substrate.

I never really understood how a snake would associate you being in the cage with feeding time if you also take them out to hold and for cleaings- probably more often than to get in and feed them. I could see if you never handled them and only got in their cage to feed them and maybe to clean how they might associate you with food. I dunno. Maybe I'm just lucky with my BP.

I do think that if you use a loose substrate you should feed outside their cage.