FPE ?

Most FT target testers are preset to test at 5.5FPE (7 joule) mimicking a WFTF at 55 yards.
So whatever that works out to be is what I’d use.

I use about 11.5fpe while my buddies 97K is sitting at around 10fpe. Both work very well.

Are you trying to use lower FPE than 10 or 11? Any particular reason? Any wind will wreak havoc if you got down below 8 FPE pass 30 yards, it’s not good as it is at 11.5 FPE. 

I've noticed, for spring guns 10-11fpe works well giving a more behaved shot cycle and predictable wind drift. In a pcp it may be beneficial as you can have a lighter hammer strike and possibly better ballistics.

Targets should be tuned to fall to 3.5fpe if shooting 10fpe at the muzzle. A light headwind will slow down that round considerably.