3% is not much…
Can you give exact values of the indicators you are talking about ? Is it the average rxlev for all the cells in the BSC ? Or the distribution of handover causes ?
It is strange to talk about radio QoS on a BSC : the QoS is normally related to the Air Interface, meaning it depends on the radio conditions between your cell and the mobiles… (it is not always true, but in your case, uplink and downlink levels are related to air interface, aren’t they ?)