Saying all these things about shape is all well and good.. But I believe the second most dominating force to the shape of a pod (after gentics) is of course enviroment. It may not change things like colour and general shape, but beyond that it effects nearly everythng else.
The biggest contributors are going to be the growth size of the pods and the remenants of the flower that causes the unmistakable scorpion tail effects. I have found when I top water my plants over the folliage and pods I end up with alot more elongated and geometrical pods and when I water roots only the pods end up more twisted and gnarly with tails.. Are the flower remenants getting wet and breaking away earlier allowing for longer and smoother pods, vs the rings remaining hard and holding the (7 Pot / Scorpion ) shape alot longer.
Pods that grow fast and large also have a greater chance of either breaking the flower ring and growing smoother, or at the opposite end were the flower holds, ending up looking very pumpkin shaped with the indented tail hanging out.
Same with the style of the flower, in some varieties I see the tip of the pod fatten up the style almost growing from inside it making the long pointy tails were on others were the style has snapped off the pod tail seems flatter and short.
I know for most this is not new information but when pods that are stable seem to look so different when grown in different parts of the world environment has to have some part to play.
Anyway, just simple observations of little value.