DIS: Error when checking in .msg attachment

Hi,
We are currently facing two issue with DIS:-

1.) We want to restrict the documents access when we click on "New Check-in" Via file Explorer DIS plugin. Changing the MaxResults=0 in config. solves this problem but the blank search in WCC is fetching all the 3 million documents, which is impacting the performance.

So now we have changed it to maxResults=3000. But now we are able to see 3000 documents in the DIS check-in screen. And also all users are able to see and access documents via DIS regardless of the access, security group they are assigned to. Its a security breach. How can we restrict the document access in DIS when we click on "New Check-in" OR just make it read-only as per security groups?