Tom, you may have better luck getting adjacency effects in the Jobo with Rodinal at higher dilutions than 1:50. Quite a few folks use Rodinal at 1:100 with times in a regular tank from 15 to 20 minutes at EIs from 250 to 800.
I can understand the adjacency diffusion occurring in the emulsion but the replenishment is from the surrounding developer so stand development will starve the most actively developing areas to a degree. I'd be interested to know how a higher dilution affects your process if the extended times don't bother you any.