4 days since last post.
I finally cycled the battery deeper than 18 amp hours. Took 42 out of it last night, disconnected all loads at dawn, when reading 12.2v under a 0.4 amp load.
Rebounded to 12.39v 3.5 hours later, so it does appear to be a slight improvement in performance from a similar discharge event on march 18th, but it is also a slight bit warmer outside. I'll try and get a SG reading after the acceptance stage completes later today, if the sun comes out.
Might reprogram the solar to do the US battery 15.3v Float/finish and just keep the AGM outta the loop, to see how the SG holds and overnight performance compares to 14.8v float/finish.