Late answer to this post, but I haven´t read somebody looking at this from this point of view.
I see the bulge as being there for exactly the same reason as there is a buldge on the trailing side of most secondary transfers ports.
It shapes the exit horizontal angle to give the max possible effective port area.
Wobbly mentions flow increase with the buldges, but lost if exagerating the buldge horizontal angles. This "flows" good with what I just wrote... maybe...
Bookmarks