Hey Danno . . . I don't have to make a drawing. I didn't think the attached photo was the same as my stem, but upon looking closer, I can see that it is the exact thing. If you look closely at the wedge, you can see the end of the horizontal cylinder I've been yakking about. The wedge, instead of being solid as most are, is hollow, with about a 3mm wall thickness. It must have a thinner wall thickness than the stem, because I can see the stem above it. I thought the stem end was another structure inside the wedge, but that must be incorrect.
The purpose of the cylinder is to give a true lead for the stem bolt, even as the wedge moves from back to front to tighten the stem into place. Nice engineering, really.
So yes, I just have to get over it and really whack on that stem bolt. With luck, I won't blow the cylinder out the bottom of the wedge.
I will try that right now, now that I know what I'm looking at.