To offload 900 Band, another way could be
1. to set CRO =0
2. to set ACCMIN for 1800 equal to LAYERTHR for 1800MHz (ACCMIN for 900Mhz could be -104dBm).
Idle MS will camp on 900Mhz and during call setup Locating will transfer the calls to 1800Mhz (for those who satisfy LAYERTHR).
1800Mhz will become congested earlier than 900Mhz. During congestion 1800Mhz will transfer new calls to 900MHz through Assignment to other cell.