I am teaching myself the slap and pop technique. I can pop pretty well, but am having some occaisional problems with slapping. Sometimes when I slap, I get an undesireable harmonic tone. I slap and pop at the end of the fretboard, but when I move my right hand back slightly (closer to the bridge), I don't get the harmonic nearly as much, but It's more difficult to pop. Any suggestions on what I'm doing wrong?