I installed the 1" diameter one just in front of the L.A., you just have to work it around with your finger a little to make it uniform.
It does leave a little gap, so I used a 3/4" where the gap is betweeen the body and bezel. I tightend the body until the 3/4" GITD o-ring filled the gap.
I had to put the hex of the bezel into my rubber padded vise and tighten the body with a thick rag between the jaws of an adjustable wrench as I didn't want any marks on my new light.
It works great and the thicker 1" GITD o-ring really lights up.