Piecewise periodicity structure estimates in Shirshov's height theorem

The Gelfand–Kirillov dimension of $l$-generated general matrixes is $(l-1)n^2+1.$ The minimal degree of the identity of this algebra is $2n$ as a corollary of Amitzur–Levitsky theorem. That is why the essential height of $A$ being an $l$-generated PI-algebra of degree $n$ over every set of words can be greater than $(l-1)n^2/4 + 1.$ We prove that if $A$ has a finite GK-dimension, then the number of lexicographically comparable subwords with the period $(n-1)$ in each monoid of $A$ is not greater than $(l-2)(n-1).$ The case of the subwords with the period $2$ is generalized to the proof of Shirshov's Height theorem.