The links between defects and other entities are stored in the link table in the project database. When you link a defect the link is created to the entity specified not to the test that created the entity. So if you link a defect to a test run the defect is not linked to the test so the link icon will only show up when viewing the test runs. I think that the best way to get the information that you are looking for would be to use the analysis module and create a project report. The other option would be to file an enhancement request with to change how QC handles defect linking. The enhancement request may or may not be accepted and would not be available until a later version or patch.