In theory, all of the corners suck up a little energy and cause a little distortion, but I have no idea how noticeable it would be. If I nominated someone to test it and see how big of a difference it makes, it would have to be you my friend.
Not that I wouldn't do testing to see.......but it's not going to happen with this project.
I have bookings for this system already and I haven't built it yet
Ply delivered tomorrow & drivers on their way.........
Oh have done that to much my self, hiring out before I am done with the system. Can be seriously stressful when something goes wrong, and something usually does.
The smoothness of the bend will actually be more important in the throat section than in the last "scoop" section.
I still think that the two part corner is the best compromise if you don't have Flexi-ply laying around. But if you have to hurry, the jbl-style corner will also be fine. In the end its only marginal differences in the sound with these long wavelengths. If it had to be a Hi-Fi "full range" scoop the smoothness of the throat section would be quite important.