AFAIK, setpos is broken for MP for some reason, been so since OFP-times, no idea why
Maybe someone with more MP experience can answer that (hey, guys, why isn't there a separate MP-scripting forum for ArmA? Huge differences often between MP and SP, after all?).
As to the shooting-over-sandbags, Blanco here :
http://www.ofpec.com/forum/index.php?topic=28856.0 had the same problem. All I know are good ol' OFP solutions (setdamaging the object), which obviously don't work for ArmA...hm. Beats me anyhow.
Do they fire over the sandbags when standing up? Have you checked to see if it's a specific "won't shoot over" issue, or a spotting issue? (i.e., try putting units behind the sandbags, and then revealing enemies to them using the
reveal command, and see if that works?).
As to the name, Wood Fence...heh...many of the default objects have flaky names, like "Shed" and "Shad", "Wire", "Fence", etc. Gives ya a good ol' tingly feeling of home.
Wolfrug out.