For slap I am more comfortable on a 4 w/20 frets; on a 4 there are less *wrong* strings to accidently whack, making for better accuracy- and the shorter 20-fret neck allows me to place my right hand closer to the middle of the speaking length of the strings(subjective, but IMO the string is more responsive to plucking/slapping, etc the closer you can get to the very middle of the length).
I also suggest developing control over relying on a compressor. THAT said, I use a comp 99% of the time...
Edit: Just noticed where this was posted- I am NOT Ray R. Never have been, never will be. Pardon me...
