InstallShield 2012: installation fails if IIS Virtual Dir is set to the same property name as component destination

I have a specific property (set in a custom action) that is used to store the directory location where the web app should be installed. I have set the value to "destination" for Feature as this property and also "Virtual directory / content source path" for the web application in the Internet Information Services pane.

The web application was copied correctly to the destination folder. If I were to use a different property, say [INSTALLDIR], the installation finishes without error, but the IIS virtual pointer is pointing to the wrong location (INSTALLDIR does not match my installation location as I am installing multiple web applications and each one has its own property)

The installation will come back and the following is found in the logs:

CommitChanges for path 'MACHINE/WEBROOT/APPHOST/Testing/MSOW' and physical path 'C:\OtherInstalls\MSOW\'.
CommitChanges failed with the following HRESULT: '-2147024891'.
Error with IISRT: -2147024891 CustomAction ISIISInstall returned actual error code 1603 (note this may not be 100% accurate if translation happened inside sandbox)
Action ended 10:48:08: InstallFinalize. Return value 3.

Do I just need a different property for Virtual Dir? Or am I just confused?