The naming I see goes "FM2_1.fmb" "FM2_2.fmb" ... "FM2_10.fmb" "FM2_11.fmb"... etc.
This is less than ideal, at least on my system, because the next decimal, eg. "10", does not sort after "9" but, rather, after "1" in the "Save Backup As" dialog opening from the main menu File/Backup; the Restore dialog sorts the same way. Thus two issues:
1) For manual backups, one cannot just look at the last entry to find the next appropriate name, but has to "pick through" the list to ascertain what the next incremental file name should be.
2) Since _which_ backup one restores from can have considerable impact, it seems worth making it as easy as possible to avoid mistakes.
One of my file managers sorts the way I'd hope and/but another sorts the way the dialog box does. The world is mysterious.
Just FWI. Thanks
Rufus