Try consciously getting up onto the balls of your feet/your toes more as you set up to pop, makes the initial movements of the trick a little more deft and can really help with kickflip based tricks, certainly should encourage a bit more ankle movement as you flick as well. If i'm being lazy my default foot position is dead flat, and this can make quite a few tricks feel a little dulled...good for heelflips though.
I've got the flattest feet going, and skate nothing but flatground...once you find what works for you, it's not really even a disadvantage.