  We study the $T$-dual completion of the four-dimensional ${\cal N}=1$ type II
effective potentials in the presence of (non-)geometric fluxes. First, we
invoke a cohomology version of the $T$-dual transformations among the various
moduli, axions and the fluxes appearing in the type IIA and type IIB effective
supergravities. This leads to some useful observations about a significant
mixing of the standard NS-NS fluxes with the (non-)geometric fluxes on the
mirror side. Further, using our $T$-duality rules, we establish an explicit
mapping among the $F$-terms, $D$-terms, tadpole conditions as well as the
Bianchi identities of the two theories. Secondly, we propose what we call a set
of "axionic flux polynomials", which depend on all the axionic moduli and the
fluxes. This subsequently helps in presenting the two scalar potentials in a
concise and manifestly $T$-dual form, which can be directly utilized for
various phenomenological purposes as we illustrate in a couple of examples.
