On cue for PE5 is to keep the chin and chest on the floor at all times. My guess is that this cue is designed to prevent people from lifting up off the floor.
I find that if I keep my chin on the floor, my neck ends extended past neutral, but if I keep my nose and forehead (just above the eyebrow line) on the floor, my neck stays close to neutral. If I were to take these postures to a handstand, the forehead-down position is much closer to the straight line I'd be looking for. The chin-down posture would be out of alignment.
Is it ok to keep forehead down if the neck stays in neutral (not flexion)?