Trouble resizeing the mini map
What resolution are you running the game at? I just checked and if I lower my vertical resolution enough I stop being able to change the mini map’s vertical size.
As Khinsanth points out, it may be that your resolution is too low to support increasing the height of the mini map. The UI probably has to allow a set amount of space for the quest tracker and won’t let the minimap go up into the space.
Yes unfortunately there is not much customization in the UI and it only allows for sizes based on your resolution,