Did I make it 2.5"? If I did, I might go with 2" the next time, because if you scroll to the top here, you can compare my A with the one on the actual helmet, and I think mine ended up a little large and a little tall. Also I don't know why, but the extra bold I added may also not be a great idea. I overlaid the letter directly over the original though in Photoshop when I was making it though, so I'm not sure why the real one should appear to have thinner lines.
Also I got the color totally wrong. The real helmet and the one in the film is a much darker blue. I'm not sure why the one in the promo shot I used is so light but they they're auctioning some stuff from the film off and I saw the real helmet in the background of a shot under normal light.