Alex,
A better FER will certainly lead to a better SQI : the FER is part of the SQI computation. FER is mostly depending on the radio quality and the codec’s protection to interference.
But a better SQI can be achieved also with a different approach, such as less handovers, or better codecs, as suggested by Bilal.
A paradox : “Better” codec offers less protection than a “resistant” codec… The former will improve voice quality under good radio conditions, the latter will improve voice quality in a poor C/I situation.
Regards,
Pix