Yes, you've correctly identified the dimensions of the problem.
I often dive with a reel (left d-ring) and sometimes with a stage (left & left chest).
The camera & flash are naturally positively bouyant. That's nice for attaching to the butt ring, because they stay out of the way of the legs when kicking. But an entanglement there would be really nasty. On the other hand, maybe the entanglement problem isn't so solveable. Also, I think there would be a lot of tank banging on entry, which was fine for the camera alone but I think has potential for damage with the flash.
The other natural option is the left hip d-ring, but again the rig is positively bouyant, so its going to want to interfere with, e.g., ease of clipping and unclipping the depth gauge.
I could add a weight to the camera to make it negative, but it would get all dangly...
What I'm leaning toward now is clipping to the left hip d-ring for entry, but moving to the butt d-ring for travel. (Exit doesn't matter much.) That still leaves the nasty entanglement problem, so I guess until I find a solution I'm leaving the camera behind if I go near any existing line.
This is really an issue of balancing risks and benefits, so I thought soliciting wisdom from the experienced would be a help.