After over 30 tries and a lot of pain and suffering trying to figure out reversal processing, I found out that the first developer has to very aggressive with a silver solvent added, and I had to give up on the light exposure step and use a fogging developer instead (Kodak FD-72). The light exposure step turned out to be the thing that was causing inconsistent results and a lot of confusion. I found that I was getting uneven exposure across the whole roll. Some of the frames would appear to be properly exposed with a normal strength developer. Once I tried a fogging developer all the shots became much darker, and I had to make the fist developer a lot stronger. I wonder how people have success with the light exposure step? I certainly failed there.
I'm still not totally sure if I have it dialed in yet, but for normally exposed FP4+, I found that 1:5 Rodinal with 1 gram Sodium Thiocyanate per liter with 11 minutes of rotary processing at 20C seemed to be approaching correct. I set this aside a few years ago, but I plan to get back to it, and compare what I have to Ilford's recommended process. I was using Dichromate bleach, and the amount of chromium rinse water it produced that I had to haul off to the dump got to be too annoying. I might try a different bleach process once I can convince myself I got everything else right.