Neither the relative level of the direct ("Dry") signal nor the room ("Wet") signal's level will change as long as you leave the bus you send the wet signal to @ 0dB.
Thank you Dietz. So if I understand correctly, adjusting that little circle, after switching to bus routing, controls how much of the MIR "wet" signal goes to the bus? And best to keep that circle @ 0 db? Sorry for beating this, but it has always been a source of confusion to me.... 😕