Diamond essentially laid it out. Both Gegogi and I have experimented with NPA and cologne mixing with good results. 5 parts cologne to 1 part NPA. Letting it sit isn’t absolutely necessary, but I’ve found that the smell of NPA and the cologne tend to coalesce into something greater than the sum of the parts after a few days in a cool, dark place.
Just be cautious. NPA packs a lot of androstenone, so anyone under 24ish should try a larger amount of cologne per part of NPA. Maybe 6 or 7:1.
-D4