I believe it was a post I read by BFL the other day in one of MexicoWanderers thread about charge controllers MPPT break even or something. about how his T-1275 needs about 15.5V daily to keep the SG up, whereas his 6 volt GC2's were pretty much good at 14.8V to keep the SG up, daily.
Would not at all be surprised if these bigger 12V jars need more oomph to get the SG up there and topped off, due to greater internal resistance to charging. Evidently charge controller voltage is not a one Voltage fits all batteries.
Will be very interested in seeing your results on the 14.8V charging for a week.