Neighbor to neighbor handover success rate can be low due to many reason.
1) HO Defination, if paramater are not defined correct. Action:- check parameter similarity for rest of the neighbor of same type.
2) Cell Load, If the destination cell is loaded HO will fail and cause will be Ho Block. Action:- decrese priority of this neighbor to neighbor relation. or Ho Margin as temp solution.
3) Target Frequency, If there is co channel or adjacent interference this may cause poor HSR. Action:- Check for frequency plan and increase HO margin if this is not a first layer neighbor.
4) Hardware, This is easiest to find. U will find all the incoming handover to this cell showing poor i/c HSR. Moreover the performance of the sector will also show degradation in this case.
Neighbors should be defined very carefully. since Excessive neighbor defination will cause these kind of problems.