I guess you could adjust the curve/gap of the reeds to see if you can get a better attack pattern. I would be intensely interested in what you learn about the way the gap and curve affects the attack of the notes. Its a fairly rare player who even tunes his own melodicas much less adjust the gap and curve, hence the rarity of good information on it – but I’m one player who has tuned a good bit. The curve and gap adjustment is bound to be tricky for the low notes – the relationship between reed mass, gap, air velocity and column pressure. Proceed methodically, take pictures if you can, you have my attention at least.