ideal x-pipe positioning for performance gain?

[Danger]

I've read through a ton of x-pipe threads but none seem to indicate what the best positioning would be for maximum performance gain - not talking sound here, just added hp/torque. I have a 3.0 engine, just wondering if anyone could be more specific than just placing it where the resonator is. I know we are not talking huge gains here, and I know sound is the main draw, but wanted to do this mod right, and based in performance gain. Thanks!