I know that it has long been believed that the ESB helmet had way more flare than the ROTJ helmet and that they must be different sculpts. Tyler D. has done a great job arguing the "same mold" case.
I was looking at my DP97 recast and the DP97 is known for it's total lack of flare. Just with holding it up and applying some subtle pressure I realized a couple of things.
1) The T-visor on the ESB helmet is a bit narrower at the top and a bit wider at the bottom. By spreading the mandibles a bit I was suprised by how much extra flare magically appears.
2) On the other hand, the ROTJ helmet has an overall narrower opeing and is even skewed a bit to one side. That drastically reduces the flare on the helmet.
3) Lastly, on a purely concept note, the ESB and ROTJ helmets both have the same dent on the forehead. If you wanted to show a different helmet, to the point of sculpting a brand new one, why would you keep the exact same dent?? Obviously some things on the costume were changed on purpose. The rifle. The cape. The flame thrower. While some others just recieved a new coat of paint. It stands to reason that the helmet was meant to have a new paint job but they got a different guy to trim to new cast and install the visor. After all, Darth Vader deflected Boba's shot and caused the dent in the first place. I doubt that Boba shot his "new" ROTJ helmet just for old time's sake.
Just my take on the subject anyway.