I don't get what you are saying about the balls making it shorter, mine start just below where the bottom side of my penis meets the rest of me.
I think it makes sense - it is longer along the bottom because the top meets the rest of me in less distance than the bottom side.
I realise that isnt a very good description :/ but i can't think of a better way to put it really.
Maybe this will help:
\|
Imagine the left, slanted line, intercects the right, vertical line.
The distance between the top of the slanted line and where it meets the vertical line will be shorter on the top side of the line than on the bottom, because of the way it slants.
So, the slanted line is my penis, the vertical line is the rest of me, and when you think of it that way, couple in girth, and bingo, it makes sense.