Pitch options for rectangular tarp?

Doesn't matter for most pitches. For example you can pitch a diamond shape with either,
tho the rectangular tarp will be asymetrical, but still just as tight. The right size
retangular tarp may end up being more efficient since the human body has a a long and
a short dimension.

I remember one guy had a custom rectangular tarp made with the tie outs at a place where he could set it up as a square with the edge tucked.

I use a bivy more for protection against misting and extra warmth. The material of the tarp has very little to do with it since the bivy comes no matter what.

Steve Evans has a video with 3 different pitches of a rectangular tarp (Episode #9):

http://www.suluk46.com/videos.html

He's using a small poncho tarp (5 x 7 ?) but should be applicable to a larger tarp.