I don't know the program (Musictech - I work with the Kontakt accordion and Hohner Gola accordion, also for Kontakt). You are an accordionist, so you're aware of the fact that left and right hand use the same volume more or less. Of course in midi interpretation there mist be a balance between the two and sometimes you need to adapt things to your purposes.
This is the way I normally deal with that balance:
don't treat the accordion like a piano
use two totally different systems for the upper and lower voices
use two different midi channels for right and left hand
Acting thus will give you the possibility of putting in different volumes (CC1, CC7, CC11), which means that you have independent control over the expression in both hands.