I think Marmit's dome looks way too big and much too long. And while Sideshow's isn't perfect, I think it's closer to looking right than Marmit's or any of the other domes I've seen.
And I think maybe Maulfan's right about the dome being changed because the casting process. It was probably significantly cheaper to make the dome a bit smaller because it maybe used a different casting process or machine, or used much less material. I'm not familiar with casting, and I'm just guessing based on my experience with printing. Sometimes if we design a book at a certain irregular size, say 9"x12", the printer will come back to us and say, "you'll save half the cost if you reduce the size to 8.5"x11" (the standard letter size)", which is really just a 1/2 inch on one side and an inch on the other. Not a big deal, right? But it's a significant change in price because there wouldn't be as much paper waste since they can gang up more pages on a single sheet. And yes, as a designer it's a hard choice to make because you have the chance to save a good bit of money (not just pennies), but compromise the design you had envisioned. Ultimately the client decides to save the money, and the piece ends up not a strong and impactful as it was first conceived.
I imagine it was something like that with the casting.