When you have eyelash extensions applied, your lash tech will look at the shake of your eyes and determine what style will suit you best. All lash sets are mapped out to create a shape tailored to your eyes and moat sets use at least 4-5 different lash length Sizes, to give a more defined look that created the right balance for your face. If you look at false lashes they are usually made up from different length to fit around your eye, lash extensions aim to do the same thing but only more natural.
Some lash maps are Doll eyes would suit hooded eye shape, cat eyes would be perfect monolid eyes and Kim K style would suit round eyes and almond eyes get the pick of the bunch as they suit pretty much any lash map...