domain mapping plugin is mapping to incorrect url eg www.example.com when it should be www.example.c

We are using Domain Mapping Plugin on our website (http://imglobal.me/discover/) but it seems that it is not working correctly. When user try to point their blog by setting up blog ip address.

Let me explain by the help of an example:

Our blog is running here: http://example.com/best (Multisite Blog)

Suppose user 'test1' has got his blog url like http://example.com/best/test1

Now if user 'test1' login into his blog and set domain mapping plugin for his domain test1.com according to domain mapping manual(here https://premium.wpmudev.org/project/domain-mapping/#usage)

But when user test1 open test1.com in browser, it is pointing to main site that is http://example.com not http://example.com/best/test1 so can any one suggest what mistake that user test1 is doing ? or how can we avoid such issues ?