Trying to use _unit inArea _trigger to determine if a unit is inside a trigger does not work correctly.
It does not always produce the same result as [_trigger, _unit] call BIS_fnc_inTrigger or _unit in list _trigger, especially when trigger length and width are not equal.
The command seems to confuse trigger length with width and vice versa.
Create a rectangular trigger with size a = 100, b = 50. Name it trg1.
Create a rectangular trigger with size a = 50, b = 100 at the same position as trg1. Name it trg2.
Teleport the player around. player inArea trg1 will always return the same result as player in list trg2.
Can confirm this.
It seems like the inArea command somehow always assumes the bigger number to the width of the trigger.
As long as A > B, it works fine (even when rotating the trigger).
If B > A it will mix them up.