[QUOTE=coachrick;5156447]It's not the knot
, it's the slack between the knot and the clamp that must be addressed. The rocking/pulling motion, done very carefully, is the way to cinch the string.
I agree with the above statement completely. I also used to have a problem with the final mains being rather loose until I got better at tying off the knot to cinch the string tighter. The following video really helped me out. At about the 30 second mark he shows how to cinch the knot which tightens the last main. I owe the video author a big thanks.