Chromatic Fingering Dilemma?

Hello,

Exactly five year ago in December 1998, we had very good discussion
about CBA figering patterns in CBA -System C and B, and especially as
it applies to French model accordions with the registers behind the
keyboard. I didn't participate in it. I just got an idea then that
playing French chromatic would be a "cool" experiment to follow.
Now, I have my own beautiful and very good French chromatic and would
like to know what are yours discoveries in that area?
Are there interesting books that would teach French methods of playing
CBA
with emphases on fingering patterns? 

I keep learning small Czech's CBA with registers on the top but still
have problem to find buttons without hanging my head down. I use five
fingers. May be it would be better to use only four fingers without
the thumb in the French CBA situation? May be a few of you have
experience already with French CBA's? Please give me a light to go
forward!
 
It passed five years from that time and many new owners of CBA's have
tried the four and five fingering methods. What is your opinion on
that subject after five years exposure to the chromatic button
accordions?

Best Regards,
W.D.