Which kind of proves that in many ways it wasn't the mission itself that was the problem in and of itself, it was the way it was approached. You know the best way to take those bunkers? Don't go straight at them, sneak up to the wall and then move along the wall to take them out at knife fight range. I've breached the perimeter killing loads of enemy many times doing this testing the mission.
I've just had a look at the mission and the only place where two M2s could possibly hit you is if you attacked right between the firing lines of two M2s that were about 400 metres apart covering different areas. I'm guessing you were attacking from the North East? Its hardly the mission makers fault if you choose to "attack across 30 metres of open ground" (your words) into the ONLY place on the entire map that can possibly be hit by two statics