Your charger is fine for what you are trying to do
Hi Landoman, I looked up the specs for your battery charger and it actually states that it can take up to 55 hours before the charger automatically goes into float mode, but it also states that the maximum total battery capacity it is designed to charge is 120Ah.
While you have around 145Ah of total battery capacity, and you are only just above what the charger should be able to handle, so it should be fine but will take longer to complete a full charge cycle.
The fact the charger goes into float when in the NORMAL setting but not while in the AGM setting may simply be caused by the slightly large battery capacity than it is designed for.
In any case, because it works properly in the NORMAL setting, I personally would just just keep the charger you have and leave it set in the NORMAL setting at all times.
The only difference between the NORMAL and the AGM setting is the voltage used in the final stage of the ABSORPTION mode. This is 14.4v vs 14.7v and is pretty well irrelevant because both voltage levels will get both batteries fully charged.
The only suggest I would make is to carry out charging your batteries with the battery charger a little more often.