I experienced this kind of situtation in some network coverage area before, we find MS can have several situtations need to check :
1. Handover ARFCN receiving power level ?
2. Handover ARFCN SNR ?
3. Handover ARFCN BSIC situtaion
If you find more handover failure statistic at some area is caused by (1), then, this means some bad coverage happen on this area, we need to check with AGC lever we use to make sure that AGC algorithm in Handset is correct, if this is a new MS design;
if you find more handover failure statistic at some area is caused by (2), then, you need to check how many different network or ARFCN plan at that area, you also need to statistic their power level to understand any interference over the spec. of MS that MS can not handle, it mostly happen with situation there are several networks at some area with several repeater;