There a guy over on this thread...
http://forums.electronicarts.co.uk/battlefield-3-pc/1444436-hud-not-scaling-correctly-eyefinity-2.html
saying in post #35, and I quote...
Rather silly (but works!) fix:
Dont run the game in full screen mode. Switch out of full screen, then you can resize the game window by dragging it just like any normal program window. You can drag it to be basically like full screen, but since its in a window, it appears to look proper.
You lose some FPS and performance by running in window, but *shrug* seems to be OK for now..
It's with regard to the HUD markers.
I haven't tried it yet as it was late last night/early this morning when I came across it, so I can't confirm it.
It's a pretty gruesome workaround but it might be all we can do till there's a fix or a patch.
Just thought I'd pass it on. If someone could give me some feedback on it, it would be nice because I'm stuck at work here for another 8 hours :(