[untamed]

Originally Posted by GreenSpottedPuffer

Or maybe because you can let more flow from your smaller sump into the larger one and therefore not allow the auto top off to kick in even though evaporation is still the same.

But maybe both answers are wrong. Im not entirely sure how your sumps are set up!

Bingo! That valve controls the water level in both sumps, but evap replacement only happens based on the main sump water level. It was totally unplanned, but kind of neat when I figured it out.

You'll have exactly that same relationship between your fuge and the sump.