When I tuned my Melodion, I learned that setting the correct reed clearance is a big part of the process. If your reed clearance is high, that particular reed will sound louder- but it may require significantly more air pressure.
Ideally every note would have the same reed clearance. This would allow for equal air pressure across the keyboard. However, human hearing makes higher pitched notes sound louder, so higher reed clearance on the lower notes and lower reed clearance on the higher notes might help create a more balanced sound. Keep in mind that if you change the reed clearance, you’ll have to change the tuning a bit to compensate.
Also, your reed clearance should follow some kind of logical change across the reed plate. If for instance, you have a significant reed clearance difference in notes next to each other it is possible to make the notes sharp or flat due to excessive or inefficient air pressure. Too much air pressure causes notes to go flat and too little air pressure causes notes to go sharp.
Good luck with your tuning!