Hi ,
I tired that - but a light colored fill pen used in the shadows will still write over a much darker pen. The problem is not just related to distance - an object in the foreground, outlined with the heaviest weight pen will sometimes have all its outlines show through a shadow, and sometimes lines will be covered. There is no consistency to how AC handles this.
A solution is to use a hatch pattern (such as the brick pen default), but I really dislike the effect of shadows created with hatch patterns. I wish there were a way to use solid fills (25%, 50%, 75%. 100%) for shadows that would let ALL lines show through. After much experimentation, the firm I work for has made it a policy not to use shadows in elevations..