I use two full-length Photon Torpedo backups. If I buckle the can light tightly against the backplate, then I can't reach the switch either (the bezel of the backup light perfectly covers the switch protector and is extraordinarily difficult to push aside. If I leave about an inch and a half of webbing between the backplate and the can light, no problem.
Another thing that helped was adjusting the can light hose clamps to sit higher on the canister, which drops the height a bit when mounted on the harness (this also extends the usable length of the canister to trap the long hose a bit better when stowed).
Another thing that helped was adjusting the can light hose clamps to sit higher on the canister, which drops the height a bit when mounted on the harness (this also extends the usable length of the canister to trap the long hose a bit better when stowed).