Tempering the HSPU on parallettes

So, I'm rather proficient at stomach-to-wall headstand pushups but I just made parallettes and have been trying to work the full handstand pushup (back to the wall) ever since then and it is truly an entirely different beast.

Is there any way I can scale down the difficulty of the full HSPU (without the building up books/mats thing) until I can get more than 1?

It really feels like my shoulders are going to fall behind in strength/size until I can be able to do them and I don't want everything else to progress far beyond my shoulder strength.

Don't go all the way down, but go beyond the parallettes?

Do sets of 5, going as low as you can on every rep, until you can go all the way down?

I'm going with the negatives and "go a little higher" approach for the time being.

Another question while I'm at it, I'm using the wall still, on parallettes, does it matter whether I face the wall or not as long as I'm doing the full ROM via HSPUs?

Facing wall tends to be better form but it is possible to do them correctly either way without parallettes. However with parallettes, there tends to be a necessity to arch when doing back to wall because of angle of where your feet are on the wall to where your hands are on the parallettes. You can align your back to slide against the wall but there is an odd angle involved.