DHW re-heat start & DHW delta

[MEKadan]

This is most likely not HeishaMon issue, but in case anyone happens to know the logic behind the following in my WH-SXC09H3E8.

According to the manuals (which are lousy, btw) the DHW start should occur when DHW Temp < (DHW target temp value + DHW Heat Delta) and where DWH Heat Delta is a negative value.

This should give e.g. for DHW target temp 55 and delta being -5 a starting temp of 50. However, the pump seems to start at 45, regardless of what I put to DHW target. Tried only values > 50 this far. Starting temp is in all of those cases 45 degrees.

Is there some setting overriding this or what?