It's possible that you're being too cautious and hanging around on a long string for a bit too long. The long string, early tillering stage is really only to check that nothing crazy will happen when you brace it. At the heavier weights, it's far better for the bow and far easier for the bowyer to get it up to a full brace as soon as possible.
As an example - in an ideal world you'd take your roughed out bow (which should be virtually finished before it's even seen a string) and put a tight long string on it, pulling it to about 6" or so. If there's no horrendous hinge, or one limb isn't wildly stiffer than the other, it's on with the short string at full brace. That initial brace shape should tell you almost everything you need to know - where the weak spots are, where the stiff spots are, what the string alignment is doing and so on. You unbrace, sort the issues out, brace it again. Keep going until that brace shape is perfect - movement in the mid-limbs, nothing happening in the handle and reasonably stiff tips. That's when it goes onto the tiller and you start working it down to draw length.
Otherwise, with a long string you're being fooled the whole time - the tips will look stiffer than they really are, the middle will look weaker, the string alignment will be off compared to how it will end up and so on.
The only person who knows what that stave wants to do is you, but if you let the long string guide you down weird paths you'll end up having no idea what should be happening, and will start forcing what you want to happen onto the stave.
Remember that countless bows have been made with HUGE amounts of twist, bend, warp and so on. Your stave looks really clean and pretty straight considering you opted to follow every little grain movement.
