Directional cover (like a REAL sandbag)

I was wondering if it was possible to code a wall-like terrian/overlay type object in a way that it reduces the damage of any warhead (by a specified percent) that passes through it, and a way to nullify this effect if the unit is on a cell adjacent to the cover object?

Basically, my thought here is that you can have a GI, per-se, who is behind a small wall, not so big as to block shots, but it provides some cover, and he can shoot out just fine, but enemies that shoot at him will do less damage (the reduction of damage will be determined with a flag like "CoverPercentage=").

Could this be possible? I remember seeing a post about using the UC logic to simulate trenches, but I had something different in mind.

If this is too complicated to code, maybe you could make an object where a unit can walk through freely, and whenever inside will recieve a defence bonus, like Dawn Of War Trenches, if you've ever played the game.