Scapula form and HBP

I was wondering what the scapula should be like during HBP (PE1/2/3) when the body is close to the ground.

It's pretty clear that we should aim to max protraction when we're up, with arms completely extended, but what about the other end of the movement?

Should we strive for total protraction as well or should we allow them to flat out (or retract)?

Also: are they supposed to depress at some stage, or should it kept neutral with regard to vertical alignment?

During all the push up movement you need to use a depressed and protracted position.

Maintain the protraction on the bottom part is the most difficult part and you need very strong serratus anterior. As you are lowering down, the chest is elongating itself , to reach the complete chest elongation (from an anatomical POV) you need to retract the scapula also moving the elbows upward, if you can move and elongate the chest without retract you are demonstrating a very good serratus anterior strength. 

All clear, thanks alex87

is that considered as failed to prove mastery if i lose protraction in last few reps (HBP/PE1) ?

I'm not sure what you mean alex. If you put your arm out in front of you while standing, protract your scapula, then try and touch your hand to your shoulder without letting the scapula tilt anteriorly, your hand is going to be miles in front of your shoulder. Now try the same with your shoulder retracted.  You can't maintain protraction at the bottom if you're going for full ROM. 

Just let the scapula move dynamically - allow your scapula to retract at the bottom, and fully protract at the top (at least try to).

As for vertical movement, depressed all the way throughout, yes.

A very quick search gives:

https://www.gymnasticbodies.com/forum/topic/11817-hbppe2-and-hbppe3-protraction/?hl=%2Bpush+%2Bretraction

Lots of info there, thanks all!

So the bottom line would be: strive to protract as much as you can, knowing anyway that you won't be able to fully do so when chest is going on the floor.

Does it make sense?