David:

I think the first aluminum P-80 mount was designed for the HotSpot.....to get the engine as close to the thrust line as possible, the lower half was larger and thus put the engine deeper than the upper half......then followed the purple anodized "Hotspot" mount which had the same asymmetry of the ring, but had longer ears (mounting lugs) to make full use of the wood plate under the glass that the mount screwed into......

Even the later Gary Mueller(Jet Tech) mounts with rivnuts were not symmetric.....

Other than that, I see no reason for the asymmetry