Your AFM distance should be "actual landing distance" which is calculated from crossing the 50' screen height at the threshold (displaced threshold, if applicable), throttles to idle, touchdown after about a 1600' to 1800' flare distance (50' screen to touchdown) and MAXIMUM braking with spoilers, if applicable deployed. Test pilots proved this could be done in that distance. "Legal Field Length", aka factored distance, aka 60% rule is supposed to give some allowance for pilot technique, etc.
GF