With square heel
Being a heel with more packaging, you can drop more cowboy. Even up to two fingers above. Your presence will not be diminished by the trousers.
And with sneakers?
The ankle length is the one that works best. Try not to cover the shoe and expose a finger skin. Let them fray a little so that the set is more informal.
With flat shoe
The same thing happens with sports. It is enough to cut approximately one finger above the ankle, since its shape leaves part of the instep in sight and lengthens the figure without problems.