There are a couple common complaints about the kings and you just expressed one of them. To help the stone work better economically flatten the stone before every use quickly so you clean out any swarf that accumulates. Once the pores of the stone get clogged we call this loading and the stone won't cut or grind nearly as well.
Yes a slurry on the stone helps the stone cut so as you're finishing the quick flattening job just leave the mud on the stone.
If it's still not working well enough for you try a better stone like the Imanishi dragon 800 which I really like a lot.http://www.chefknivestogo.com/im800grst.html