Actually I'm a righty. I'm guessing you say that based on my light on my SBR. I mounted it low like that on the right for 2 reasons.
1...with the way I have my sling mounted on the left side of the gun, and the Troy from BUIS, there isn't a lot of room for the light in the high and right position that I typically run on my 16" uppers.
2...with the shorter barrel I actually try to fully wrap the vertical grip so I keep my hand away from the muzzle. That puts my thumb right on the back of the flashlight.
Totally makes sense, it was the light in combination with the ambi safety that got me wondering.