+1 what Bob says.
I set my csinks up for flush and marked the cages with red fingernail polish so I could find flush again after using them for countersinking under a dimple. Even so, using the practice piece to check first, the flush setting has moved a few clicks over time. I also drill and dimple a small piece of aluminum the same thickness as the skin I'm planning to use to gauge the correct depth of the underlying countersink (also on scrap first).
I've also resorted to using a deburring tool when room is an issue or I want to slowly get to the correct depth, and definitely for 1097 rivets for plate nuts.
==dave==