If I wanted a 2 flavor mix, I might start at 5% of
Flavor1. Maybe it needs a bit more, so increase it to 8%. Good or not?
Maybe add
Flavor2 at 2%. Increase it to where you want it. Taste Good? If yes, taste one last time and then
throw it in a drawer for a week or two.
If you don't like that 10% mixture, decide where to go.. all the time keeping notes. Maybe add a third flavor. The possibilities are endless.