This video from Vortex explains- and
shows, the differences between FFP and SFP scopes.
At long range, the reticle will be thinner on the target with a SFP scope, which will allow for a more precise point of aim. Subtensions on a FFP scope remain constant throughout the magnification range, which make it superior when ranging is required.
http://www.vortexoptics.com/video/fi...nd_focal_plane