It might be worth noting that where you stand with respect to your amp would affect your sustain. The same principle that causes feedback, could be kept just under that threshold, or even an intentional controlled feedback. Footage of S.R.V. and Hendrix (among many others) frequently shows them playing in front of and facing their amps.
[FONT=Palatino Linotype]"Bust a nut!" - Dimebag
"Imagination is more important than knowledge." - Einstein[/FONT]