  The $s_\pm$ and $s_{++}$ models for the superconducting state are subject of
intense studies regarding Fe-based superconductors. Depending on the
parameters, disorder may leave intact or suppress $T_c$ in these models. Here
we study the special case of disorder with equal values of intra- and interband
impurity potentials in the two-band $s_\pm$ and $s_{++}$ models. We show that
this case can be considered as an isolated point and $T_c$ there has maximal
damping for a wide range of parameters.
