– remove TCH interferences (co channels)
– activate DL Power control and DL DTX in the whole area (= not in the cell only, but all the neighbours), for all codecs.
– ensure first-ring neighbours is well defined and MS can do the HO at the right time.
DL Quality is not an issue if it is less than 5, in case of BBH. Indeed, if less than 5, it does not impact the voice quality that much.
Set your DL PC to reach an avg dl quality of about 3. With such settings, the interference/noise level of your network will be reduced greatly.