I agree that having a configurable margin of some sort would be intersting. I have a fairly large system (4x Quattro 10ks), and the power draw of the inverters themselves is ~400W+ continuous.
I’ve found on low PV days, the system will buy power during a peak period, because the consumption forecast didn’t account for the continuous power draw of the inverters themselves and the system hits the min SOC too early in the day (https://community.victronenergy.com/t/dess-slowly-discharging-battery-when-scheduled-to-keep-target-soc-flat/)
Outside of adjusting the DESS algo to include this continuous power draw, the margin idea may be another work-around.