From my notes on your terrific twills workshop, determining epi is clear, however I am not sure about ppi. You say twill needs 45 degrees for drape, but how do I know when my ppi is balanced…. I always look for the “little square spaces” for plain weave, but does that apply to twill?
The easiest way to see if your twill is balanced is to take a square piece of paper and fold it into a triangle. You will then have a perfect 45 degree angle. I put that on the fabric and check my diagonal. If the angle is low you are beating too hard, if the angle is high you aren’t beating hard enough and if the angle is right on with the paper, you are beating just right. This reads like Goldilocks and the 3 bears. :^) Hope this helps.