...upgrading to the slitted disk?
IMO, the slitted disc is by no means an updrade...
A massive downgrade is what I'd call it.
The slits let some of the vapor pass around the matrix percs, a very silly design choice IMO.
I'm pretty sure the slitted disc ones were earlier models, with the slits being there to allow the water to drain back down. Having the vapor bypass the stereo seems to have been an oversight with that design...
Why does the water level bother you?
After a hit you can tilt the tube around a bit if you absolutely have to have it all settle as low as possible, but the amount of water in the tube isn't changing, just where it rests.
For me, I'd consider it a minor aesthetic issue at the worst, definitely not something I'd go out and look for an inferior tube to correct.