Simple way to check your current dies for the #6 screw head size:
Drill a #27 hole in scrap, find the largest die which has a tip that fits in the hole, and there you are! Make a few test dimples in that scrap and check screw head fit. A "too small" dimple die set won't make a deep enough dimple for the screw head (of course make sure it's an aircraft screw with 100 degree countersink angle, from your kit). And a "too big" dimple die set won't fit the correct hole size.