Yes, the scale display on Custom Maps shows the distance of the full span of the screen, and it is my own idea. I feel that it is easier to estimate how large a part of the full edge-to-edge span I am trying to estimate rather than trying to guess how many times a short line fits between the two points.
Note that the usual map scale line also is only in one dimension, typically horizontal, so my new scale display does not lose to the traditional map scale in that way either. But adding both width and height distance on the screen at the same time would take quite a bit of space from the map, and ideally the scale display should not take much space. So I didn't want to display both at the same time. Such a display could have been a bit confusing as well.
But I do agree that things are easier if both dimensions can be viewed. So you can switch the direction of the scale display by tapping the rectangle in the scale display. It alternates between showing the full screen distance vertically and horizontally.
I hope you like it.