I would start with a 1/2" but I feel you will seea problem with the release if you go longer,you will most likely need to shorten it because I really don't see you being able to anchor the release hand on you face if you don't.
That form sure has come a long way,good job.
You may also try a little more headforward approach as well,just to se if you can hit the anchors and see how it feels.
You are at a point where tweaking little things to test and see what works best for you can be extremely helpfull.
This is kind of what I am talking about.
