I think Del is right... I've a feeling (I'm far from experienced here, mind) that it's a common thing to imagine you're drawing a normal bow, and just pull further when actually you should change the way you're drawing completely for a heavy bow.
Also.... If you swap the weight bias, and lean into the bow, weight on the front leg, you start to get more pushing power, rather than relying on the pulling strength only. I can imagine with some forward lean, and some focus on changing where your drawing hand ends up, you'll be inside those bows with ease.
Gorgeous bows though, really clean looking!