RXQUAL(0-7) is not the measure of “speech quality” instead it is the measure of Received Signal Quality and it is calculated from BER(Bit Error Rate). Speech quality is measured differently by different systems e.g. TEMS SQI, MOS, SQI in stats and it is calculated from FER(frame erasure rate) and several other factors. RXQUAL doesn’t depend on the speech codec used. But SQI definitely depends on the codec. You can say HR gives worse speech quality than FR and EFR at same RXQUAL. So, there is no point of having different RXQUAL scale for different speech codecs.