Hi bluray,
Not a dumb question at all and I have the solution.
The BJC banana plugs should fit all the way in the binding posts. The problem you are having is that you did not strip the wire properly and "jammed" it into the banana plug when you were assembling them and the loose wire strands is causing pressure and the tip of the plug to expand. This is the job of the collar.
Take the small screw out, take out the wire, re-strip it and make sure the wire is perfect with no loose strands sticking out. Re-assemble, insert without jamming the wire in, secure with the small screw and then tighten with the locking collar. The collar does not need much tightening. What gauge wire are you using?
