I have a larger personal space than non-PTSD people. However I have a more "offense" than defensive approach. I have been known to turn around and stand and look people dead in the eye with sheer annoyance, or just the sheer insanity that runs around in my head. They generally are the ones who want space after that. I've also leaned back into people, stumbled back and stepped on toes, been so sorry. Thrown my purse over my shoulder while they jump back. I get the occasional HEY, to which I answer, I'm sorry, I didn't realize you were so close. I can't recommend an offensive approach because there is always the possibility of a nut who wants an argument. But most people want nothing to do with a person behaving badly. They don't mean to be behaving badly. I am the one with a larger personal space.
It also works very well, a tear in my eye as I near panic, to turn around and say, "Excuse me, I have panic attacks and if I could have a little more space it would help. I'm sorry to bother you. " Every time people have had genuine compassion for me, offered help, all sorts of things. In stores that have the electric cart I take it because that creates space and non one is in my face.

I hope you can find the right answer to establish your needed and much earned personal space.
Sincerely, Hidden1111