A fundamental question in information theory is to quantify the loss of information under a noisy channel. Partial orders are typical tools to that end, however, they are often also challenging to evaluate. For the special class of binary input symmetric output (BISO) channels, Geng et al. showed that among channels with the same capacity, the binary symmetric channel (BSC) and binary erasure channel (BEC) are extremal with respect to the more capable order. Here we extend on this result by considering partial orders based on Rényi mutual information. We establish the extremality of the BSC and BEC in this setting with respect to the generalized Rényi capacity. In the process, we also generalize the needed tools and introduce \(\alpha \) -Lorenz curves.