The positivity conjecture for constrictions

A constriction $(B_0,A_0)$ is called positive when a punctured vertical neighborhood of it lies entirely in the interior of a phase-lock area. Consider constrictions in the first quadrant

$$(B,A)\in\mathbb R_{\geq0}\times\mathbb R_+.$$

For the corresponding transition matrix $Q$, let $b$ and $c$ be the two triangular terms referred to in the source.

The positivity conjecture. Every constriction is positive.

The paper proves that the relevant ratio is real and gives a criterion implying positivity when $c/b>0$, but the universal positivity assertion is not resolved in the supplied text.