Late model 1100s and 1187s use a so-called "one piece" gas ring. It's actually two gas rings. They are interlocked together. Be sure to reinstall them with the gaps on opposite sides to prevent pressure bleed off. The flat end goes towards the breech, and the stepped end towards the muzzle.
These can be readily replaced with the older two-piece rings. I've never found a need to do so, but some guns run better with the older rings. I suspect the owners were not paying attention to the gap alignment of the new rings in many cases.
I believe the Trap T's all predated the "combined" two metal rings. You are missing a ring or the two seperate rings were replaced with the 1 combined ring. From the description you gave of the 1 ring, I think you are missing 1. You should be able to tell by looking at your other 1100's.