How come you don't just separate the locations of the SCV's and the massing units?
Placing a small area at the top of the map to build things or use the SCV's to mine, and make a square location of what units are targeted by the mass attack function that would exclude the area where the SCV's were?
It's entirely possible that he wants the map in such a way that you can actually attack others' scvs, or their buildings. Maybe you can build defenses for yourself.
In that case your scvs must be near your military units.
It's also possible it doesn't matter since he hasn't posted since the 3rd.