Can't export games saves

[locksoft]

Here's the problem: I've played Frontier (Elite 2) for some weeks, and I wanted to transfer my saves on the Switch (uaeall2).
Problem is that fsuae doesn't really saves on the .adf, but instead creates a .sdf file format in another folder.
I tried to add "writable_floppy_images=1" to the config file but nothing changed.
What to do?
Thanks

EDIT: Hmmm... it seems it works, but only if the .adf file is not compressed (zip). Elsewhere nothing is saved. Is it correct?