I found I had to apply a little heat to the calves to give them a small twist, now this is not without danger and you would need to practice on other ABS plastic, many use a hot water bath but I use a heat gun but with caution you can go from slightly moving to molten mess.
Some shin issue threads
Cricket used a magnetic closure, I've seen a few do this
Cricket also did some hot water bath adjustments to the armor, you may pick up some tips
References for mobility cuts