It is a bit a matter of taste but generally when A4=440 (or 442 or something else) has an amount X of tremolo (in cents) on the MM register then you gradually tone down the amount of tremolo to somewhere between 2/3 and 3/4 of X and the same for the next octave, ending at between 4/9 and 9/16 of X at A6 (normally the highest note on a PA). Going down from A4 the tremolo goes up to about 4/3 of X by A3 and stays roughly the same for the next few lower notes, and when you have an accordion with very low nots the tremolo goes down a bit again for the lowest notes.

I tend to set my "compromise" value at 70% (about midway between 2/3 and 3/4). This applies to all values of X, whether it is 4 cents, 8, 10, 12, 16, 20 or even more...

When you reach these "mathematically correct" values you may still wish to make small adjustments by ear because the tremolo (for adjacent notes) has to sound right (that's more important than whether it is mathematically correct).