We can use the MultiBand in the network in order to reduce the use of frequency 900Mhz. it’s commonly known that 900 coverage is big than 1800Mhz coverage so the 1800 band should serve for capacity and 900 layer should serve coverage, access and Handover.
there are many parameter to manage the trafic between this two layers for example nonBcchLayerAccessThr and nonBcchLayerExitThr and nonBCCHlayerOffset
I can helpe you if you provide me with sufficent data about your network site location trafic and ….