Assessing the effect of knee flexion angle, Klein et al. (1996) measured the moment arm as a function of ankle joint range of motion in 10 cadavers. (strengthandconditioningresearch.com)
In the lowering phase, external oblique muscle activity was greatest at knee flexion angles of 60 — 31. (strengthandconditioningresearch.com)
Assessing the effect of foot placement, Escamilla et al. (2001) compared the horizontal leg press performed with a high foot placement (90 — 100 degrees of knee flexion in bottom position) and a low foot placement (20 cm lower). (strengthandconditioningresearch.com)