I too got the AFEX system - I actually purchased three of them, all with the bigger style "Receptor". I was afraid the smaller style receptor would be less satisfactory because my penis might flop out of it, so I have never tried one of those.
Even with the bigger one, however, my penis has frequently flopped out and this resulted in wetting the underpants part of the system.
I got what seems to work better with the receptor. The input is round, of about one and five eights inch diameter. I found a plastic spray bottle of this diameter and about 6 inches height. I sliced a lenght of about 2 to 3 inches (If asked, I could measure what I have been using) and poked this into the entrance to the receptor. It was a trifle too big, so I made a cut in it about 1 inch long so I could squeeze it smaller where it pokes into the receptor.
I am not sure I have made myself clear. Ask if you like.
This has worked very well for me. If I know some urine is coming out - it can happen - I stand up, or lean forward. The idea is to be sure the urine flows by gravity DOWNwards, and not BACKwards into the underpants.
I hope this suggestion may help someone here, and would appreciate suggestions for anything better.
GER