Upon publication of the original manuscript (Prudil and Welland 2017) discrepancies were highlighted in Eq. (50) [equation (1) here].

The equation in the original manuscript (Prudil and Welland 2017) erroneously included a factor of 2 on theta and read:

$$ \cos \left(2\theta \right)=\frac{\sigma_{\alpha \gamma }}{2{\sigma}_{\alpha \beta }} $$
(1)

This equation should read as below:

$$ \cos \left(\theta \right)=\frac{\sigma_{\alpha \gamma }}{2{\sigma}_{\alpha \beta }} $$
(1)

This error has since been acknowledged and corrected in this erratum.