You're correct. The hex file you see is not the size of the hex file the software uploaded to the Arduino hardware. Unfortunately, with the current releases (including 13b), the real file size isn't available.
If you're having problems with the program size exceeding the size of the flash on your board, you have two options:
- Reduce the program size, or
- Use a board with more memory (e.g., Mega2560, Due).
To reduce the program size try to:
- Simplify the model
- Remove unused blocks
- Reduce the size of signals and data
- If you enabled it, disable External mode