Hi,

That's because you have some Ngons, I guess.
You can try to check uniform mitering in the bevel panel. That Slightly deform the mesh, but avoid ngons :)

Hi,

Here's two tutorials to make custom depth pass
http://www.grabiller.com/site/index.php ... s_eng.html
http://www.bernardlebel.com/tutorials/X ... thPass.htm

I hope that's helpful
:)