I was wondering this exact thing while I was welding in the aTm rings copperhead fab made me this weekend. In my head it made more sense for them to mount flush but the rings' O.D. was about ~1/4" smaller than the I.D. of the wheel and I figured a 1/8" gap was a little too much to fill and maintain near-perfect centering so I welded them in below the surface. I f'ed up the very outter edge in a couple of spots but I'll probably go back and fill/grind them back into shape. I'll post pics tonight.

Also, I only got 4 aTm rings originally and decided to go with 5 rims so I'm gonna need to call copperhead and have em whip me up another ring.