The current wiki states it's used for portals which are small and ring shaped, but i'm not sure whether that makes it distinct enough to be its own tag rather than being aliased to portal

It's very under tagged, but seems to be consistently used for stuff where the portal looks fitted onto the body:
post #4636748post #4844471

As opposed to stuff like this:
post #4820370post #4774450post #4772939

The most common mis-tag I saw was ring-shaped/circular portals, so at worst it might need a different name.

It might be better served by aliasing it to portal and just tagging the more specific things its used for: portal amputation, portal penis, etc.