Shoot us an email and we'll get you an appropriate shim for the specific size bars you have, or check our Accessories page if you know already.
In short: because it's a worse material for the job than glass-reinforced nylon, I'll explain...
This right here is why I hate the bike industry...we'll figure out a solution for you, but I'll explain here...
YES! The quick-release interface for our lights is reversible, so even if you flip our mount upside-down you can always insert the light right-side-up. This means you can put our mount on the right side of the stem and still keep the light centered, the lever will just flip up when closed instead of down, no problem.