As questions about the internals of a specific program are (logically) pretty code-related, I think it would not really fit Crypto.SE.
Crypto.SE has no problems explaining the workings of crypto, and maybe even handling some code-specific questions related to crypto-implementation. But - according to my personal point of view - questions that ask how a specific program implemented it's individual file-structure is less cryptographic and more code-related. In other words: if you'ld ask how AES crypto works, this is the right place… if you ask what individual file format/structure some crypto-software uses, it's less appropriate for Crypto.SE.
A little tip aside: Have you tried contacting the authors of AEScrypt? Most software developers (like me) have no problem sharing information about the file-structure their software uses. I'm pretty sure the AEScrypt software developer(s) will provide the most precise information about the AEScrypt file format.