Merge Requests difficult to review code

For certain Merge Requests my group does, the Code Reviews are very difficult.
We are running a simulation and have several Subsystem versions that sit next to each other that a user can select. When a change is made to this Subsystem we don’t replace Sys.1, we add Sys.2, even though the two are 99% identical. So when we do a Merge Request Sys.2 looks like all brand new code, and the Review just lists the hundreds of files as new. This often takes up so much space in the Review it blasts the limits of the amount of code that can be reviewed, and other associated code that is changing can’t be seen in the review. We need to:

  1. Tell the Merge Request to Review the code not as new but to Review the code in new dir /Sys.2/ against the code in directory /Sys.1/ so we see just the deltas for the one or two files that may have changed. We have not found anyway that even hints that this is possible.
  2. Not review the Subsystem code at all, so we can see the other associated deltas. We have tried to use the .gitattributes file to tell the system not to review certain directories (/Subsytem/Sys -diff) or (/Subsystem/Sys binary) listing directories with and without an asterisk , (and other permutations) to indicate everything there, or to tell it not to review the file components (.abc -diff) or (*.abc binary) but we can’t get this function to work.

Any Suggestions?