I agree with your first paragraph, although that's probably a different topic...
Yes, it can be arbitrary, but I feel like before this year it was almost always on the bottom guy. This year it seems to be more evenly split, but no hard data behind that obviously, and to your point I have seen a few instances where for example the situation doesn't change but they will hit the bottom guy first and then the top guy like 20 seconds later. But at least in that scenario if they both get hit then it might help prevent your first scenario...