@SpokeyDoke...
I earned it first time with platinum boom together with slick sls. But I got an wing buddy at the lake with slick dlab and sls boom also got it. I use harness and I am mostly hooked in. But I got it in summer Lulls while pumping like an maniac all the time

to get on foil. And so it was for the dlab guy. So I think the boom diameter wasn't the problem first line.
once u got it and u don't recover fully it can swing back in next heavy session. BTW way I used this Thera bar too and it was to painful to twist that thing. I also got both golfer and tennis elbow. On both arms

I really overdid it. The exercises to resolve it, is extensive muscle Contraction. its Meant to do with the Thera bar. U can also do it less painful and cheaper like shown. Bring the weight in upper position by helping ur fxxxxxx hand with the other and then slowly Sink the weight. Repeat. So u don't need the flex bar.