Users can add as many profiles as they wish, so Rhino has the tools to avoid self intersections. But it doesn't make any guesses for you... Anyway I rarely use Blendsrf if I want a precise blend, then I would use networksrf because results are much more predictable and allows fitting within tolerance... The same I think is true in MoI that Blend is good for quickly sketching but usually a poor choice for modeling to spec within acceptable deviation...

jonah