I think I understand what you are saying, but I think we are talking about two different things (maybe?)
I can’t see how you are calibrating from over here, but from what I have gathered the camera and the monitor (your calibration target) are fixed and don’t move during calibration. You have constraints that prevent you (or your customers) from moving the camera or monitor, and since you are only interested in calibrating the distortion you can get away with this. Furthermore you only need to have accurate distortion calibration in the area where your single calibration target (monitor) is visible. (Please correct me if I’m wrong on any of this)
I wanted to bring that up because what you are doing is a special case situation, and I wouldn’t want anyone who comes along later to think that you can get a full camera calibration from a single view.
Back to your comment on getting the Aruco pattern into the corners…
Since you are using the monitor as a calibration target, and you need to be able to distort anything you (later) see in the monitor, it is important to get the calibration target to fill as much of the monitor as possible. This way you get corner points as close to the edges / corners of the monitor as possible. I think your trick would have applied to the standard chessboard target too, or at least seems like it should.
So what’s the big deal about the Charuco calibration target? What do I mean by "it lets you get points closer to the edges/corner? Well, in a typical camera calibration process you will capture a large number of calibration targets from different angles, filling different parts of the image, etc. The idea is to get points in every part of the camera’s image so that the resulting calibration will be valid / accurate for any pixel. Getting data points in the central part of the image is easy…typically you have way more than you need. Getting points near the corners / edges is much more difficult. Why? Because with the standard chessboard calibration pattern you have to be able to see the entire pattern for any of the points to be used. If a single corner isn’t visible, none of them get used. This can make it very difficult to get points that cover the corners. The magic of the Charuco calibration target is that you don’t have to see the full calibration pattern, so you are free to move the calibration target however you want, moving it so that you get something in the corners of the camera image.
Sorry for the confusion on that.