One way you could know is to have an experiment
. time yourself and see how many minerals you got for all four placments. That would be the only way to tell.
It's the same issue that comes up with ramps/chokes. If it takes you longer to get to your choke than normal, you might not be able to wall it off in time to stop a rush. Timing is one of the most time-consuming parts to making a balanced map.
IMO.