Ok hold on a second...
I'm going to chime in with something obvious, but no one else has mentioned it...
In both images that show the MadVR stats (which you say one has the boxed problem and the other doesn't) MadVR is outputting at the same resolution. The "draw" line in the OSD proves this. Refresh rate is different but resolution is the same.
So, unless you have been monkeying with the display settings, timings, or anamorphic settings in MadVR, I think the problem is not with MadVR.
You may have different timings or scaling settings set in your video driver configuration for the video modes associated with those "boxed" refreshed rates. Check there. You say 60Hz displays fine, but 59Hz is boxed. Check the settings in your video driver for overscan/zoom/etc for those refresh rates.
Secondly, it could be the projector doing this without involvement from anyone else. You might need to check there.
You can test these theories by closing MC completely, and just changing your Windows desktop resolution and refresh rate to match the refresh rates and resolutions you're seeing in MadVR. If the problem is with the video driver config or the projector, you will still see "boxing" even when MC is not running.
If there is never any boxing with MC closed, then show us screenshots of your MC Video Display Settings, and screenshots of your MadVR config for "display mode" under "devices". There will be little use in more talk without seeing those screenshots...
If the problem only manifests when using MadVR, then your MadVR display settings will need to be unborked.