okay there's 2 things you may have done wrong here,
1st: you must have saved it wrong format = big/smaller size, than original
2nd: when you hex edited it you must have done it wrong, steps etc... thus giving you a different size,
*IT* must be the same size as original to work in-game, but saying this is only 1/4 of the way for it to work correctly.
hope i helped