How to check registered DLLs in WiX

I'm looking for a way to check if certain third party libraries are installed with certain versions. I want to check the registered DLLs and don't know where they were installed in the file system. In this example, I'm pretty sure they have version 1.50 installed:

<Property Id="PRIORGUID">
  <RegistrySearch Id="priorguid" Root="HKCR" Key="Prior.Encoders\CLSID" Type="raw"/>
</Property>

<Property Id="PRIORLOCATION">
  <RegistrySearch Id="priorlocation" Root="HKCR" Key="CLSID\[PRIORGUID]\InprocServer32" Type="file"/>
</Property>

<Property Id="PRIORVERCHECK">
  <DirectorySearch Id="priorversion" Path="[PRIORLOCATION]">
    <FileSearch Name="Prior.dll" MinVersion="1.49"/>
  </DirectorySearch>
</Property>

<Condition Message="This application requires Prior.">
  <![CDATA[Installed OR PRIORVERCHECK]]>
</Condition>

      

        
        
        
      

    

I basically find a library in the registry that points me to a file, and then I go through the version on the filesystem. I don't understand this method. When I use Type = "file", it returns the directory the file is in instead of returning the full path to the file itself. Does it always work like this? It also means that I have to know the name of the base file. If there was a way to split the full path into name and directory, then I could do FileSearch without knowing the basename?

Is my method reliable? Is there a better way to do this? It looks like this will be a common problem. I am using WiX 3.

Thanks.