Resolution
In case anyone else has this issue, the end result of my research is that once the battery output gets down in the 12.3 range the XM1800 is only putting out AC voltage in the neighborhood of 95-100 volts. The residential refrigerator can't start on that and it cuts out on low voltage long before the 2 minute delay built into the AGS. Obvious solution is to manually run the generator but in my case I had been planning on being away from the coach for a couple of days. Ultimate solution that'll result in the AGS and inverter actually functioning in tandem in a residential refrigerator scenario is to replace the inverter with a "true sine" inverter such as the Freedom X which, I'm told, will provide 120v regardless of DC input.
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