As far as I know, all organizations of baseball and softball state that there is a violation when the fielder at first base is hindered from receiving the throw (or words to that effect). Limiting it to the plate area is not accurate because you could have a throw from F1 who fields the ball halfway up the first base line that could lead to a violation.

I vaguely recall years ago a very lively discussion on a baseball umpire board about a throw coming from the shortstop, and how there can be a lane violation in that situation. It got rather ugly...

True...

Probably better said (in both sports) that it comes into play on throws coming from the DIRECTION of the plate, not just the area. There are differences in the minutia of the rules (most specifically regarding the need for a quality throw) but the idea is the same in both sports.

I think y'all just need to drop any "directional" references as such is completely irrelevant to the rule and possible violation.