Question about French bass system ( 3+3)

[Ganza]

My second-hand Piermaria 318 (L?) has a French bass setup.
It goes like this:

Minor 3rd (one row down)
Major 3rd
Bass
Major chord
Minor chord
French 7th chord


What I'm trying to show is that the minor 3rd, instead of being in the same row, is one row down.
Does anyone know why this is? And, do you think it makes bass runs easier to play by being displaced by one row? I'm not sure that it does...
The diminished button is already displaced by one row too of course in the French system, and on my accordion, the Minor 3rd is ALSO displaced by 1 row too!
Help!
Luckily, the 4 sequential method books I have (which came with the accordion) from the 70s/80s, written by Andree Astier and Joss Basseli, use the same bass system as I have in my Piermaria (including the Minor 3rd being displaced!)

 

[dunlustin]

Ganza, dont know if this helps but Ive always assumed the minor third is there to avoid stretching down
(eg: C, jump F,Bb then Eb) for a minor triad or run and the offset is to make the fingering friendlier.
This is particularly true when the run starts on the fundamental row.

By the way at least one famous Accordion Method writer tells students to avoid this minor third row until theyve acquired a solid technique
as it is the easy way out.
His version of having to suffer to be beautiful!

You mention the French 7th and the displaced Dim button so you probably know already but:
eg F7 = F A C Eb removing the root leaves A C Eb - the French 7th but that is 3 notes of a Cdim chord.
So, you can use the IV7 minus the root instead of the Idim to similar effect. (eg Cbass + (French) F7)
If you think of a dim chord as piled up minor thirds you can pick these straight off the treble side of your CBA.
For example the 4th note in the above pile would be F#, next button along from A C Eb.
Some would say you can get by for quite a while without the Dim row.
Heres a man who knows his way around his Cavagnolo - all 5 fingers too:

more use of inner row here

 

[Ganza]

Hi dnlustin
Thanks very much for all that useful info and the vids - nice!