My suction cap should fit then, as it's around 100mm in diameter if you want it. I also have a gopro one but I think the larger one is better.
I pushed out a shopping trolley dent on my r32 from behind. I just removed the rear seat's arm rest, from what you wrote should give you access as well.
I also have a compressor, but I think it's more to do with the -60 degree liquid CO2 at the bottom of the can.