i have a zone with coordinates (-318.6, 20.8, 729.3), size 250 100 250 and rotation 303.8892.
my position is (-1112.3, 43.0, 698.5)

result: IsInsideBounds returns true
expected result: IsInsideBounds should return false

private bool IsInsideBounds(Zone zone, Vector3 worldPos)
{
    return zone.collider.ClosestPoint(worldPos) == worldPos;
}​

seems to do the trick.

Merged post

i see you changed it in the last update. thanks k1ll :)