It just goes to show the metric is basically useless IMO. Receivers inline or in the slot are going to have an inherent advantage, defensive coverage affects it, offensive scheme, etc. It's too context driven to draw any meaningful conclusions.
Anyways pure yards of separation is somewhat overrated IMO. A pass catcher's job on a play is to create leverage that gives the QB a throwing window. There is no way to measure that on a computer chip like NextGen tries to do.