Hey. I’m a beginner at slap myself. Just about 4 months now so I’m no expert so my advice might not mean anything. But I had the same question and never did get a straight answer. Kinda depends on the bass and the player. Everyone said higher action than bluegrass. So I put height adjusters on my bridge and ended up lowering it. My opinion is as low as you can without buzzing.
Right now, this is my string height. Measured in millimeters at the lower end of the fingerboard with digital calipers. Distance from bottom of string to top of fingerboard. G=8mm. D=9mm. A=11mm. E=12mm.
That depends also on nut height. I had the luxury of getting to meet and watch Joe Fick live a couple weeks ago. His action is almost nonexistent. Very low. Compared to mine anyway. But I still play bluegrass so I cant go as low as I want to right now.
.
