For hot air to escape at this gap, you have to have intake on the other side(front), so the fresh- cool air could push the hot air out on the back, like Haibike has done.I still reckon the gap is there for airflow for the battery/motor.
Hot air from the motor will not escape by it self just by putting only one gap-hole in the back, you will need some kind negative or positive air pressure inside the system, so the cooling would be effective, similar like in computer case systems.
Don't see here to be the case.
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