This also might not catch the case with only fixed loc and scale.

We need the information whether self._dist should be called with loc and scale (this case) or without (next case).
I think we don't have that information yet.
IIUC:
test case:
1) `_dist` is stats.norm, and `self.loc=2, self.scale=2`
2) `_dist` is frozen stats.norm(loc=1, scale=2) and we should return self._dist in this case