The preview can be a bit confusing at times because the gizmos are drawn over everything else in the game so they ignore the geometry.
This can be somewhat alleviated by drawing additional lines which expand or contract depending on the distance to the surface but it also increases the visual complexity of the gizmo making it look not so great anymore.
I made an alternative version which shows you more so you can replace the content of the script and see if you like that more: Pastebin.com
Thial
joined
Just a stalker modder