I've noticed some different ways to play slap bass. Some play with their right arm in a 90 degrees angle to the strings. (Flea) And others play with their right arm almost horizontal. (mark king, victor wooten) I've been trying both ways. I think that I play fastest when doing 90 degrees, but I produce some more clean notes when doing it horizontal. And also 'double thumb'ing is easier when playing horizontally. Have any of you given it some thoughts?