So, after a couple years of trial and error I can consistently produce an excellent pie using commercial yeast. I've now begun to incorporate natural starter (Camaldoli) in place of the commercial yeast in the usual way - 10% of total dough weight. Unfortunately, my brilliant oven spring has disappeared. The starter is the single change I've made. Recipe is basically - KAAP, 61% Hydration, 10% Starter, 3% Salt, Kneading roughly mirrors Varasano's with two autolyse periods, balled straight from mixer, 12 - 16 hours in proofer at roughly 77F. Rise is better than double. The Camaldoli culture is fully active and I emulate, generally, Bill's (SFNM) starter regimen. Pies bake at 750 (2Stone). Taste is markedly improved with a nice mild tang, but oven spring is nonexistent. I'm clearly missing something here - Any suggestions? Is there something obvious I should change. Thanks in advance.