I hadn't thought of that. That makes sense. I have heard the "lower is better" advice, too. I had assumed that it's safer for the occupant because you're (theoretically) a bit less likely to spray glass fragments into the person's face by breaking the window lower down. Well, that was my brilliant theorizing, at least.
You'll spray the occupants with glass fragments no matter what. The good news is that auto window glass is tempered, so it breaks into tiny dull pebbles instead of various-sized razor-sharp shards.