The aes-bios.bin has no relation between the two versions, but nevermind that.
Scale is 2 by default indeed. Changing it to a larger value is not possible. But that is something else then changing the aspect for stretching. Scale 2 is just the double size of the original size.

I never had crashes in fullscreen since the fix.

You can check two more things, and if that does not give a clue, I am done with it.

In x-terminal:
should result in:
Start gngeo to make sure we use the right one:
This should result in a fullscreen start of the game, with stable behaviour when using the volume buttons.