Hi I think you setting should be at 418. In the general configuration for house batteries is series/parallel. 2 6 v batteries are connected to raise the voltage to 12v but this does NOT increase the amp HR capacity. Just the voltage. When the 2 "banks" of 12V are connected, the amp hr is increased.
The following is from the Magnum ME-RC manual.
Parallel connection – batteries connected in parallel (positive to positive,
negative to negative) increase the AHr capacity of the battery bank, but
the voltage remains the same.
Example: A 12-volt battery bank with three 12-volt batteries that are rated
at 125 AHrs each. Each of the positive terminals are connected together and
each of the negative terminals are connected together (i.e., connected in
parallel). The AHrs of each battery connected in parallel are added together
(125 AH + 125 AH + 125 AH = 375 AH), but the voltage of the battery bank
stays the same (12 VDC).
Series connection – batteries connected in series (pos. to neg.) increase
the voltage of the battery bank, but the AHr rate remains the same.
Example: A 12-volt battery bank with two 6-volt batteries that are rated
at 220 AHrs. The positive terminal of the fi rst battery is connected to the
negative terminal of the second battery (i.e., connected in series). Since the
two 6-volt batteries are connected in series, the voltage of the batteries are
added together to produce 12-volts (6 VDC + 6 VDC = 12 VDC), but the
amp-hour capacity of the battery bank does not change (220 AH).
In battery banks where you have batteries connected in series and in parallel,
the rules are the same. The batteries connected in series are referred to as a
‘series string’ and the amp-hour capacity doesn’t change. Each series string
is connected together in parallel to increase the amp-hour capacity. Add the
amp-hour capacity of each series string connected in parallel to determine
the total amp-hour capacity of the battery bank.