you might want to try something like this: this will you give you (most likely) some pinching on that top edge, but depending on what it is that thing, perhaps you can get away with it.
Hey, yeah that's what I ended up doing, thought you wouldn't reply ! :D Thanks for the detailled explanation and taking your time to redo a model for me, +1 on you !
Prutsirs_JayJay you can search on Google, Youtube and even here at Polycount forum about them. There are a ton of info about constraints. Also you can check the "User Guide" of the software you use to learn about it. Hope you find what you need!