Frank, I have been doing a little testing with Rodinal as well-though not as well thought out as your testing sounds. Have been working with FP4+, going from EI of 80 to 64 and Rodinal 1:50 to 1:100 with semi-stand developing.
One thing I have noticed is the contrast is much better with the semi-stand, first attempt was using roll film, 2nd was with 4x5 sheet film. The other thing I have noted is the sharp negatives..now it could be because of the contrast, or maybe the negatives just feel sharp. One other thing I have noticed, print times have dropped quite a bit, where a negative might have taken 15 to 20 sec and required quite a bit of dodge and burn, with the semi-stand I have print times of 5 to 10 secs and very little dodge and burn. Will not say that is the difference, but could be..or maybe my exposure is better or maybe there is no need for the images that have been made.
Need to do more detailed work, but would suggest giving the semi-stand development a try. Look forward to your results.