Ok I think I have a solution! I have tried all combination of "Swap Axis", "Invert X" and "Invert Y" settings without being able to change anything! But finally I discovered that I was doing the changes in the wrong place! In fact I was changing the settings under FFB tuning of the trim elevator axis and not under pitch and roll axis! I have no idea how I didn't notice this before, but it was the only reason for the elevator trim to have an effect on the aileron axis.
So, again, thanks to everyone!
Best wishes for incoming Christmas and New Year!