To best disguise different pitches how much will the plant foot move to the left or right of the power line without giving a particular pitch away?
Or, do you think it matters and why?
Even at the highest level of 'A' ball it doesn't matter much. If you called out the pitch so the batter knew it still wouldn't make much of a difference.
If you aren't starting off from a different spot on the pitching plate I don't think it's much of a tell. Now from a mechanics perspective you don't want to be that far off the center line (relative to where you push off) no matter what pitch you are throwing but that's a completely different discussion
On a screwball some pitchers will put their landing foot very near or even outside the pitching lane. Good hitters can pick up on it, but pitchers will throw some other pitch occasionally from the same landing spot to keep hitters guessing.
What’s far more common is the third base coach reading the pitch from the grip and relaying it to the hitters. I think it’s bush league at younger ages, but it’s common as they get older and in college.