Replying to Full Tilt question

First, +k for help on this. So I tried my first pair of full tilts two years ago and loved them more than anything, they were the zebra stripped hot doggers with flex 4 tongue I believe. I grew out of them though and picked up the new ones and I just have a quick question.

So the new boots I have seem to not flex as well as my old ones, I don't think it's the flex of the tongue though. when I undo the straps and bend forward the tongue flex fine, but when they're strapped up its hard to flex and it feel like i'm not really moving. I think the problem is possibly the back of the boot is too tight and doesn't flex with my legs when I bend forward.

Sparknotes: Can I make the back of the boot looser? If so, how can I do that?

If you have any other suggestions for better flexing here's other things that may help you help me: I'm 5 7 and weigh 126. I have very skinny feet and calfs.

Thanks! and +K for help