After a lot of experimenting I’m still liking the open sound too. I’ve yet to damage mine playing that way.
The only thing I’m missing sometimes is that very dark clouded sound that the vintage Hohners seem to have.
I’ve tried putting tape over the vents in the shell and stuffing Styrofoam and even cotton into all the spaces in the end caps.
It doesn’t achieve that effect.
The part I can’t get is what I discovered by accident is if I lay the melodica down on a soft blanket and play it has a lovely warm character that I haven’t been able to reproduce.