It is known already for some time that the leading power limit of the Color Glass Condensate (CGC) expressions for dijet production can be identified with the (generalized) Transverse Momentum Dependent (TMD) factorization in the small $x$ regime. In the latter formalism, there are several TMD gluon distributions containing distinct Wilson line operators, and corresponding on-shell hard factors.
There is a natural extension of this formalism, which generalizes the on-shell hard factors to the off-shell case in a gauge invariant way -- the so-called small-x improved TMD factorization (ITMD), which allows to study the kinematic regime beyond the back-to-back configuration, and thus beyond the leading twist.
In this contribution we briefly recall the ITMD formalism, flash a recent phenomenology study of dijet production in proton-proton and proton-lead collisions at the LHC, and -- most importantly -- we report on the recent proof of the ITMD approach from the CGC theory.