Much better tone is achieved if the strings are higher off the neck. Good guitars, or in good condition, (as action is concerned, for normal playing) make lousy slide instruments. You need really high action to get an expressive sound, and dynamics. Got to a pawn shop and get a wreck with a warped neck. Your good flatpicking or fingerstyle guitar is not set up for this "rough" style. Can I suggest that you learn good chordal phrasing and study scales first? Also, as long as I am being a kill-joy, a bowed instrument (violin, viola etc.) is far superior for this sound.