I'm going to guess SFP given this quote from geargrinder:
"FFP=First Focal Plane
SFP=Second Focal Plane
FFP reticles change in size with the magnification allowing for ranging at any magnification setting.
SFP reticles are calibrated for ranging at specific magnification settings. "
And this quote from the Vortex website about their Dead Hold BDC reticle:
"Measured in MOA at the highest magnification"
I don't claim to know jack about the differences between the two but that is what I would deduce from what I've read. I'm sure someone far more educated on this specific topic will either correct what I've stated or concur.
Good luck and hope I didn't lead you in the wrong direction.