Our recommendation hinges on what you have beneath the TV. If you have a sound bar or centre channel speaker, or other objects that would cause reflections or be distracting, you may not want lights on the bottom. Only you can decide. Both work.
Good rule of thumb:
Take the screen size in inches and:
divide by 15 for required 4-sided length in metres.
divide by 23 for required 3-sided length in metres.
This works with any strips, not just MediaLight, lol.
If you are in-between sizes, you can either play the lights further than the recommended 2" from the edge or size up. If you get 2.65m, then you'd want to get 3m and trim it down.
With 4 sides, every inch that you move from from the edge gives you another .2m to play with. BTW, I know that mixing imperial and metrics is one of those awful American things like "gotten" and not believing in the germ theory of disease, so flame away.
Anyway, plugging in 55", and you'd either want 3m for 3 sides or 4m for 4 sides.