"on the glass" will make me crane my neck and go "huh?" like Scooby-doo.

Hahahaha..
I've looked this up a while back, apparently this type of fetishism is governed by the fact that there is a " cognitively Opaque barrier " between you and -the goods-
It's very similar to the operating feature of sheer fabric fetishism. (stockings/lingerie/etc)