On those kinds of UTH most put foil on the sticky part and then tape the UTH to the cage bottom. That way you can remove it if needed. Sticking it using the adhesive included can make you bend and break the internals if you need to remove it. Being taped on and foil on the adhesive keeps you from doing that.

All that said you should be fine. Foil tape will not insulate it and having it raised a bit is a good thing to do.