Pinion angle question

I don't see how. For one it will be "opposite" from one way to the other, plus, you cannot depend on the "wrong side" of the perches to be anywhere near level or the same for that matter. The measuring surface is the side that rests on the sprAngs. That's the only surface you should concern yourself with. That and "wherever" you measure at the pinion.
Exactly I don't see how either. That's why I'm so confused about it.