External radiator flow

Mounting an external rad (alphacool 1260mm supernova) on my wall today. Two ports shown will be on the left so one on top and one bottom.

Does it make a difference which is inlet and which is outlet?

Typing this out I feel like there'd be less for the pump to overcome if top was inlet and that way the water in the rad doesn't have to overcome the weight of the water above it to reach the top if the top was the outlet