Biro, Collado and Zamora's indeque ratio conjecture for series-parallel graphs

Let $\mathcal S$ be the class of series-parallel graphs. Biro, Collado and Zamora's conjecture.

$${}^{\alpha}_{\omega}(\mathcal S)=\frac 1 2.$$

The indeque ratio measures the asymptotic minimum proportion of vertices that can be covered by an indeque set in a graph class. The conjecture concerns the sharp value for series-parallel graphs; the supplied text does not state whether it has been resolved.