  We study positivity in the conjecture proposed by Lejmi and Sz\'{e}kelyhidi
on finding effective necessary and sufficient conditions for solvability of the
inverse $\sigma_k$ equation, or equivalently, for convergence of the inverse
$\sigma_k$-flow. In particular, for the inverse $\sigma_{n-1}$-flow we
partially verify their conjecture by obtaining the desired positivity for
$(n-1, n-1)$ cohomology classes. As an application, we also partially verify
their conjecture for 3-folds.
