Mandible spharm pdm

Dear expert
first,l segment the mandible,then split it into two half.
2.l choose the right part,then copy it .l cut the copy short.
3.then both part use spharm-pdm.
4. in the modeltomodeldistance the right mandible as the source,the short copy part as the target,choose corresponding point to point. shapepopulationviewer ,the attribute:point to point vector,but l found the arrow is not from source to the target,what’s the problem?