Shutting down at 11v is normal for inverters. Some just sound alarm at 11 and keep running till 10.5. There will also be a high voltage shut off such as at 15v.
The sag in voltage relates to the size of the load and the size of the battery bank, so with high amp draw loads, four batts is better than two batts. But also the type of batt makes a difference how much sag you get with 12s not as much sag as 6s and AGMs very little sag compared with Wets.
For the same battery bank footprint, and planning to run very high drawing loads, AGMs would give the least sag before hitting the 11v alarm/shutdown. IMO the 12's advantage over 6v is not as important here as that the 6s are true deep cycle and it looks like deep cycling is going to be the usual thing here.
