What I described above will never result in “proper” 240p as the term generally refers to a ~60Hz, ~262-263 line image. It will just change what is defined as the active window.
Most, if not all, MD games are not 240 vertical lines, they are 224 lines. So you can try v.active 224 also.
Although, from your description of changing to v.active 240, it seems like your display ignores this change. Possibly because you are in x2 mode, try the higher line modes and/or set your TV to PC mode. This is all up to how compatible your TV is and how flexible it handles scaling.