this came from the jl website. maybe you read it there
The ratio of W to h should not be any more than 9 to 1 to prevent tuning shifts introduced by excessive friction between the rapidly moving air and the port's surface. It should be noted that this is not a hard-and-fast rule, merely a rule of thumb to help you prevent a mis-tuning.
In short, keep the port as square as aesthetically and physically possible.