Trailing arm pivot point neglecting pinion angle?

[XGreen]

I have been trying to decide whether to change where I mount the front pivot point of my trailing arms. I will be welding the axle seats in after so I can set the pinion angle where ever I want. Is the only advantage of raising the pivot point to correct the pinion angle after a drop? I have done a 4" frame drop in the back for now with stock springs. I eventually may want to do a bit lower with some drop springs. Also I read somewhere that you want your trailing arms to point at the output of the trans. Why? mine are pointing under the trans output now.

Can anyone shed some light on the suspension geometry theory behind the pivot location of the front of the trailing arm suspension?
Thanks for any and all help.