Hi Srihari
Okay - sort of understand. Let me maybe explain some aspects of the linkage and then it might help you. As mentioned there is no way to directly link a Test Instance from the Test Lab to a Requirement, as this functionality was replaced by the introduction of Releases Module. Firstly some terminology
Test Script ( I assume this is what you are calling a Test Case ) defines the process to be performed
Test Configuration - is a variation of the Test Script - may have fixed parameters defined etc.
Test Instance - is ah executable of the Test Configuration - i.e. it can appear multiple times in multiple Test Sets
So when you are setting the either the Test Coverage in Requirements Module or Requireemtns Coverage in the Test Plan module you have the option to also select the Test Configurations that you want linked. Please see attached screenshots. I think this is what your looking for ? Don't forget you can create multiple Requirements trees to satify the types of reporting required - we do this quite often in order to report at different structureal levels
To only way to get true Test Instance coverage - which means the coverage based on Test Execution - is to link via the Releases Module. That is by linking the Test Set folders and Requirements to a Test Cycle and then change the Coverage Analysis settings to select the appropriate Test Execution Cycle.
Hope this helps
Thanks
Martin