What you are doing is fine tuning. It doesn't take much rest movement at all. If it does I'd look for a different problem. I'd guess my rest gets moved much less than a millimeter in any direction.
Think of broadheads as fletching on the front. You got your field points with fletching on the back rough tuned with paper or by sight. Now you are making the ones that are really picky fly right.
I don't set my sight pins until after I tune this way. I have a one cam bow, so I set everything square and level, rough set my pins with field points, shoot a few broadheads and adjust the rest, then give my pins their final setting.
This even worked somewhat on my old wood riser bow which won't give clean flight no matter what I've tried.
You can't expect to get exact same flight unless the field points you are using are as long as your broadheads but you should be able to get most modern bows very close.
