Victron Battery monitor doesn't jive

[steved28]

I have a Victron BMV-700 battery monitor and recently installed 4 LifePO4 100Ah batteries. I have been testing my battery heating pads (12V) usage against battery life. When the heating pads are not drawing current, there is about 1A (dc) of parasitic draw. When both pads are on, the draw is about 11A. They cycle and have been in use for a few days.
This is where I have my dilemma. I have 400Ah worth of storage, the BMV-700 knows this. I have used 269Ah of storage, yet my SOC (according to the monitor) is at 55%. The usage number also comes from the monitor. The sitting voltage right now is ~13V.
So how can I have used well over 50% of my Ah rating, and be at 55% SOC? What am I missing and what should I be using to determine my remaining usage on my batteries?

Thanks for your input.