I wouldn't worry about it. The second ring is not supposed to be for the bottom half of the case.
There are three main 'lumps' to the P1D. The bottom half of the case, the top half with the lens and reflector and the emitter/board/electronics bit. This bit is double threaded. It screws into the top half of the case with one o ring to seal, and into the bottom half of the case with the other. If you can't see the top o ring it just means that on your particular light the emitter 'pill' has been screwed slightly further into the top part of the case.