This was an issue during my first outing with my full costume on at my local con: My back plate and the attached collar plate rides up between the jetpack and the jetpack harness as I walk around. I use a Kcrp7r harness (V1.0, I think), a Fett Seven fiberglass jetpack, and RKD vac-formed armor. I think that the round cutout at the bottom of the backplate is too small for the harness to properly protrude through. Because it is such a tight fit (even tighter once the jetpack is mounted) the backplate gets pushed upwards as I walk around and gets pinched in place. It creates a ridiculous 'no-neck' look. To top it off, my neckseal dickie gets all untucked when this happens.
I am considering widening the hole at the bottom of the backplate. I am hoping that the harness will fit through the wider gap without the jetpack mounting tabs pinching themselves against the backplate.
I am also considering putting a couple carriage bolts through the harness' tube frame and through the backplate to prevent the backplate from moving upward. I cut out the access panel on the back of the jetpack and haven't found a good way to mount it back in place. This big hole in the jetpack would be an ideal spot for the bolts to protrude through the backplate.
I am also considering shortening the harness' lower mounting tabs at the bottom. Shorter tabs should mean that they won't get pinched between the backplate and my back. No pinching should mean no need for the backplate to push up to relieve the force.
Solving the neckseal problem is a no-brainer. Velcro, snaps, or outright sewing it to the flight suit is a solution I've heard mentioned many times. I simply thought it frivolous and unnecessary until now. I'll be taking care of that tomorrow.
However, I'd like to hear the community's experience and ideas before cutting away parts of this rather expensive costume.