It is very much a matter of your choice and convenience. Some set it at 100% SOC and watch not to go below safe discharge levels for lead acid 20% to 50%, knowing you have room to go down to 1% SOC (and shorten the battery life in an emergency). Some set it as 50% which tells you you are at zero SOC even you have more Ah available - in case of other users on board who may not be familiar with the lead acid details and you like them to have a simple view of 0% SOC when real SOC is only at 50%.
On my 460Ah lead acid bank I had it at 50% with very small loads and small solar
. Mainly watching temperature, voltage and the current
- not much the SOC. But in your case of a smaller bank with 40 to 100Ah safe usage capacity not to shorten the battery life, you may want to be able to set it at 200Ah in case you like to know what is going on once you are below 100Ah usage.
I found this very helpful: https://surveillancetrailerrental.co...voltage-chart/