Trick question, right?
Remember the surface wind was calm and we were directly under each aircraft
In still air, tip vortices descend and spread out away from the aircraft. In the situation you descibe, both vortices would have moved away from you.
If there is a crosswind, the vortex from the into wind wingtip will be blown back across the centreline and follow the vortex from the other wingtip downwind. Therefore, if you were standing on the centreline with a crosswind, you would feel one of the vortices pass directly over you, but in still air, no.
Easier to draw a diagram but I hope this helps.
Stout
