Hi! as far as I know, it only works from DSC1800 to DSC1800 cells, DSC1800 to GSM900 cells, and GSM900 to GSM900 cells. You can use edge handover to shift traffic between different cells. The commands to see all the edge handover configuration is GCELLHOBASIC.
When you put DL_edge_HO in 20 it means MSs can be handle to another cell when their power level are -90dbm.
Sorry for my bad English.