Image size is ambiguous

If no one provides an answer here, please file a service request. It might be that the number you found in the documentation is wrong and needs to fixed.

I think I've seen numbers for configuration size have a qualifier in the documentation saying that the numbers are approximate. When I've been asked the actual size, I think I've generated a programming file in a format that makes it easy to see the actual number of bytes (instead of relying on the numbers in the documentation). It's been a while since I've done that, but I think I might have used the raw binary file (.rbf) size under the assumption that there are no overhead bytes in that file.

I don't remember hex files including any overhead bytes, but I'm pretty sure tabular text files do not. You could compare a .ttf file to your hex file to see whether the .ttf file omits the apparently extra bytes that are in the hex file.