I have the solid couplers and they are now a smooth fit over the shafts.
I think when you tighten up the locking bolts, the shaft may slightly distort making it tougher to get off. Add in years of rusting = just about impossible to get apart. Mine were very tight. To get apart I got long bolts and put a metal socket between the hubs and forced them apart as the bolts were tightened. And I used a propane
torch. And I used PB blaster. And I thought something would break as I tightened up the grade 8 bolts.
For assembly, I lightly sanded the hub insides and just greased and slipped them together. And they have been fine for the last 5 years. You really want a sliding slip fit. Imagine trying to whack a too tight hub back on and damaging something. I think it is good to keep some heavy sticky grease all over the hubs where shaft meets hub etc....
The work boat
fisherman guys here like the split hubs. One side has bolts which squeeze down on the shaft. Comes apart fairly easy and you always get a tight hub to shaft fitment.