Yes, I already read this. However, I think it also would be a good thing to have the capability of entering the size directly for e. g. by double clicking X or Y. I often create levels e. g. for house inners in order to use the maximum space a level can provide (144×144). To be able to directly enter the number would even more speed up this process than merely be able to dragging the level’s borders. Just think about it. It probably would not harm to have both for the designer. 🙂
Either way: Please make sure not to shrink the levels accidentally by dragging and destroying maps on it unintended.