How exactly does the auto aim head shot work? I've been practicing the first one at Rassvet. I hold L1 and square, then when Snake starts to raise the gun I hold R1 as well. Seems I still need to tap the aim up just a tad. Is that right or am I doing something wrong?

I think you just need to hold square if im not mistaken? The headshot could be due to the angle or positioning of snake? I'm not sure.

He starts in a fixed position behind a tree. The runners seem to go into first person to shoot and it appears to be automatically aimed to the head. Not the case for me.

No idea then, maybe they push the stick to aim towards his head fast enough that its hard to notice?

I figured it out thanks! Thread closed. (L1+Square<R1<L2+R2<release Square)

Actually holding L1 makes it a bit easier before shooting (better lock-on because of slower movement)