Your math is correct and you should be reading slightly higher voltage reads than you are getting.
A couple of thoughts:
Are you depending solely on the meter in the panel to monitor the batteries? If so, the meter may be out of adjustment of failing. Did you adjust the Peukert exponent when installing the new battery bank?
The best way to check the voltage of the bank is to disconnect
the bank for a while by turning off the red handle switches, check the voltage
with a good quality meter from the main studs in the battery well.
Have you load tested each battery to determine if you were sold a faulty or defective battery?
Hope this helps.
With best regards,
Sailing Vessel - Cream Puff - SM2K - #275
Currently cruising - Santa Marta, Colombia
I have a battery issue too, that I’d like opinions about.