What FOV scaling is the default?


I am having difficulty understanding how Unreal 5.3 handles FOV and FOV scaling. Information online is very different from what I am experiencing and that brings me here.

My requirement:
I want to create a top down camera that doesn’t show more of the horizontal space on wider screens (yeah, it’s blasphemy I know, but I want to stop the camera from showing out of bounds regions of the map). This means that if the user scales the game window horizontally, they should be seeing less and less of the vertical space. I believe this is called vert- FOV scaling.

My experience:
I have a single camera with the default FOV of 90 deg, and constrain aspect ratio and override aspect ratio axis constraint disabled (so that the aspect ratio shows 1.777778 and the Aspect ratio axis shows Maintain X-Axis FOV).
Now, if I enable Constrain aspect ratio and increase the aspect ratio, I get what I expect in the editor, same stuff on the horizontal axis and less stuff on the vertical axis. But if I disable it again, and run from a new editor window and resize that window, I get Hor+ effect that is I can see more stuff on the horizontal axis including the out of bounds area and the same in the vertical axis.

I watched a video from a few years ago (watch this part where the screen is resized https://youtu.be/ZVEfspETs84?si=pD7oWOkAuSe3LCm3&t=288) and I am seeing exactly the opposite as in the video.

What is going on here?

I have been trying various ways to figure out what’s up and this is what I have found

My Camera is in a Pawn and if I don’t have the Override aspect ratio axis, I get a Hor+ scaling even though the default is supposed to be to maintain x-axis FOV. But if I enable the override without changing anything else, I am getting Vert- scaling as I want. What is happening here?

You could limit camera movement to prevent it to go further up or sideways than what you would allow. Does that sound reasonable?

Well, I am already doing that based on the camera FOV. But it is the confusion with the FOV itself that I want to know about. If I know for certain that the horizontal FOV doesn’t change as screens become wider, I can calculate the vertical FOV with certainty and with that I can detect that edge of the map. But for that I need to know why the horizontal FOV is not behaving the way its supposed to be.