the idea of getting more push from behind by keeping the ass end as wide as the wide point doesn't work.
Maybe that's not why we shape wide tails!
Sure a rounded pin will surf better, but not everyone worries about how their downwind board surfs. STAYING on a plane is way more important. Speed rules.
A wide tail lets you walk the board up and down controlling pitch with ease!
As opposed to having a board that drops off a plane instantly if you step just a few inches back because the tail SINKS.
There is no RIGHT answer to any feature. I develop shapes that work for me and my waves and wind.