Online Maps v2.4 has a size limit by side of tileset = 256 * 2 ^ N.
When you set an incorrect value is returned to the nearest value of 2 ^ N.
Size (in scene) can be anything (other than zero of course), and it does not restore value.
In Online Maps v2.5 this behavior is fixes. Now can be any size of tileset >= 512.

No, you can not show the full world.
We have made such a restriction to prevent the problem, when one coordinate has several positions in the scene.

You have to force it to zoom out as it reverts back to zoom level 4 on play, and you still can't get the full world to show.
(as soon as you click on the map object the zoom auto changes back to the minimum for the tilesize)

Best I can get on a full HD screen is:
tile size:2048x1024
size in scene:1920x1080
zoom:3

is there even a map provider that stretches out to zoom level 2?

        // Tileset must manually be resized to fit the screen (until asset is modified)
        tileSetControl.Resize(Screen.width, Screen.height);

Zoom level 3 (lowest zoom level possible).
3D tileset.

??