I can give you some general answers. They come from past experience—work done during other conflicts in other militaries, and work done in civilian psychiatry.
You are more likely to develop post-traumatic stress disorder when you have traumatic stress that is more severe psychologically. Yes, being in combat on the front lines is generally more stressful. But balanced against that is the fact that these guys are well trained. This is their job, their career. I think this is protective for them, to a certain degree.
Someone on CAF who is not expecting to have a rocket fall in the camp might find the experience very psychologically traumatic in some ways. So although they might have fewer traumatic experiences, they can be just as at risk for PTSD.