Where do I set the water level for new clones?

Specifically with DWC, since it is different depending on the methodology, as long as the roots are staying moist they will grow. The roots will eventually grow down into the solution, and stay there, so keeping them wet continually is not a problem with DWC as long as your water temp is good and the aeration is sufficient.

The touchy point with placement in DWC is making sure that the original rooting medium does not stay soaked. I'm sure there are clay balls (grow rocks) in your mesh bucket, but inside of there is the original rooting medium-- rockwool? oasis? If you're slick you will remove the rockwool and gently place the clone right into the rocks-- that way there is little chance of keeping it too wet.

Bottom line... make sure the roots get wet either from direct contact or from the bubbles bursting at the surface, AND make sure that the water level is not too high so that it keeps the cloning rockwool soaked.