I have a new AC180 and do not get anywhere close to the 1152 watt capacity advertised. If I plug in a small fan drawing 21 watts, the AC180 calculates that it can run for 26.3 hrs, but this is only 552 watts. This seems to reflect what I am seeing on my camping trips. I just do not get near the 1152 watt capacity the system is supposed to get. Less than half is not acceptable.
TLDR - You will never get 100% of the rated output due to inverter losses. Smaller inverters are better for smaller AC loads, while larger inverters are more efficient for larger AC loads.
Welcome to the harsh world of solar. The Wh listed on the unit is physical capacity, not usable capacity. It is due to inverter losses. Power stations that have high inverters will experience very poor performance when subjected under a low constant AC load. The AC180 is only 40% efficient with a constant load of 20W. This is due to the fact the inverter is 1800W. The AC2A or the new Elite 30 V2 by comparison would be around 65-70% efficient since its inverter size is only 600W. If you want more efficiency you need a smaller inverter, or better yet use a DC powered fan which is around 85% efficient.
See: https://community.bluettipower.com/t/bluetti-powerstation-idle-consumption-and-efficiency/25702/7