What "target SOC"? The only SOC settings that I know of for normal Self-use mode are Overdischarge SOC (Stop using battery) and Forcecharge SOC (Battery is too-low - charge it a bit from grid).
The normal priority for PV is Load, then Battery charge, then Export.
It is the SOC set in the Backup menu, which defaults to 100% and is an independent feature of what is really only two functional storage modes, Self-Use or Feed In Priority.
Now before you say that is for backup only, it isn't. When this Reserve SOC trigger is set to anything but 100%, and even if you select Backup mode, the inverter switches to Self-Use mode and uses this Reserve SOC ( when less than 100% ) as the trigger to start a charge, and if charge from grid is not selected, solar goes first to the battery.
By default for Backup / Self-Use ( using the default 100% for Reserve SOC ), when the reported SOC by the closed loop battery is 98% ( or less ) it will charge to 100%. This is done to prevent overcharging the battery ( like 99.8% to initiate charge as was done when I found this issue)
This is for the 5G HVES and the new S6, the EU version should be the same code base but I can't say for sure as I don't have the EU version.
One thing I don't like about this is it will cycle from the Reserve SOC value to 100% once triggered, so if for example one wants to have a maximum SOC of 95% it will only cycle for 95 to 100% every time it hits the Reserve SOC.
The developers in China only test in the lab and are Siloed from even support, it took me a 3 month effort to get the issue addressed and I had to Work from both Solis and BYD to get traction on this.