IMHO (In My Humble Opinion) means just that, my opinion just like you are entitled to your opinion. If the knob is so close that it is touching the escutcheon, IMHO it is set too deep. If a lot of the stem shows, it is set too shallow. How much clearance and how much variance between them is a matter of personal opinion, but the inconsistency smells of poor workmanship. As I said, it may or may not have been the fault of the plumber. I would not accept that sort of workmanship and if the contractor would not make it right, I would open the wall on the other side.