nomPDSCH-RS-EPRE-Offset

Dear expert,
when I change parameter: nomPDSCH-RS-EPRE-Offset +1 dB, value CQI report increase, MIMO usage also increase but user throughput DL desrease, any one have experience about this parameter please share reasons anh how to fix it, can we maintain or increase user throughput DL with small change nomPDSCH-RS-EPRE-Offset +1 dB or +2dB,
Vendor are Huawei and E//,
thanks,