As far as cushion goes, have you ever even watched vasek play? He hardly cushions the bag at all, he sticks his perfectly level foot out, near the ground, and the bag sticks because it has nowhere else to go.
youre correct on this one. look at the very first videos of vasek in nike shoes. he always had good crank though his clipper style changed. it allowed him develope the style that he has today.
Here's a different angle:
I have far above average crank. Nearly supercrank. I'm not very good. I've only been playing for a few months. Seriously for about two.
Practice>Physical attributes.
yes. thats why these chinese superflexible ballerinas who never heared of footbag are worse than any badcrank player.
yes, crank matters a lot. its one part of the puzzle to become a good player. i mean its just physics: put a bag on ya hand at 45 degree angle and move it up and down: it will roll off. now do same at 30 degress: it might not roll-off but it is more likely to. next is at 0 degree: the bag wont ever fall off. if you have problems doing swirls (vasek style, uptime dex) because of bad crank try this: put foot on ground so its purely flat and put bag on it. now pull your foot up. youll see how fucking easy things become just because you started with a flat foot position.
people who say it doesnt matter just simulate bad crank and see how it goes. but why should one do that? why limit yourself? the truth is the best wouldnt be the best if they had shitty crank. having an athletic/skinny body type comes first though.
to answer your question, you can increase your ankle crank. how? by practicing insides and clipper. it will improve about 5-10% by added muscle strenght but thats about it. genetics define your natural flexibility and the limits for improving, just like they define how much muscles you have and how much you can add by bodybuilding, for example. to really influence crank developement you need to be a kid in growing phase and then flex your feet often so it grows flexible and strong. all your hardcore streching after this timeperiod just loosens it so it gets weaker which is not a good deal if you ask me.
here are the good news; you CAN become good with not so good crank, but it will be fucking harder. you DONT need good crank to play and enjoy footbag. you DO need it to become one of the best. no more lies. (jorden, dave etc. have above average crank, and not "no good crank" like some people claim.) of course, form will help; of course, there positioning the foot in the right place will help, but its just not the same as having a good crank and doing these two things. i think you got my point.
in the end all you can do is live with it or find a devilish doctor who will help you out. your choice.