I think the half lead will keep the missile on the bisector of the target-SAM-point of impact angle (counting the limits due to main lobe size of SNR/RPK, as full lead will keep the missile of SAM-PoI line....)
As a half-lead must keep the missile on bisector line of
target-SNR-point of impact angle, when this angle became less than 8 degrees, the missile should leave the 4 degree limit mark and starts follow
target-SNR-point of impact angle
/ 2....
