I have found this explanation for example:
Bake the soufflé: For maximum lift, it’s best to heat your soufflé from the bottom up — in other words, the direct heat of your oven should ideally be coming from below. Also, place the soufflé on the bottom rack of your oven so it’s as close to the heating element as possible. Alternatively, you can preheat a baking sheet in the oven and place the soufflé on top of this to bake; the baking sheet acts like a heat source.
But I can hardly agree with that. Is there a way to use only the top heating element in the oven so that the top will get crust and not burned and the bottom will get baked properly? Maybe the solution is just to use narrow and taller cup?