Thank you, everyone who contributed. I can now thump on my 24 fretter as good or better than on my P-Bass.
I finally sat down and got my thumping technique to produce an excellent sound 99.999% on my P-bass. I never did this before because I don't have to slap often so I faked it when I had to. It was passable on P but quite sucked on my 5 String 24 fretter. On my P, my thumb position is/was always beyond the fretboard, on my other bass, my thumb is over the fretboard so I assumed that this was the problem.
Once I had thumping down very good on P-bass, I put on the 5-string, 24 fretter and and I could do it almost as well. This is a first. After a few days I could do it just as well as on the P.
I'll chalk it up to the P-bass being more forgiving for learning since there is no fretboard to worry about under your thumb. I guess once you can thump the string the right way, the fretboard doesn't much matter.
I'll soon be asking about popping with two fingers on one string on MM Bongo in another thread but feel free to input here.