Maybe if you sprayed the inside surface of the mozz with a little vinegar to raise the surface acidity some more, it would help? So spray with vinegar, wait a minute, rinse to remove any residual vinegar flavor. Or as another option, what if you used mascarpone instead of cream? Or a mascarpone/cream mix... something to bring the acidity down a little. Or what if you cultured the cream with Leuconostoc like you would for creme fraiche? Just throwing out some ideas. Haven't tried any of these.