deep drawing pinch trim clearances?

I'm hoping someone can help me fine tune the clearances for pinch trimming.
We have been making little cups or cans from .010" thick material. The
average final part looks like a thimble but the tolerance on the diameter is +/- .0005". We have been shimmy trimming the cans but are now trying to pinch trim and stay within the tolerances without resorting to an ironing step.
With a straight draw punch / die clearance of .0105" (one side) and a trim punch / die clearance of .0001" (one side), we get straight walls but the walls smear up and are jagged on the top.
If we taper the draw punch inward at the top of the can, we get a clean top edge but there is a little "flange" that sticks out an extra .002 - .004" thereby exceeding our diameter tolerance. The "flange extends .015 - .020" from the top.
I am about to make some test tooling changing the depth and length of the taper to try to find the right balance between straight walls and a clean top. Does anybody know what the correct depth and length of the taper on the punch should be? Or have any other suggestions?
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