Rotobrush / Refine Edge - Adjustments

Hi everybody,

I'm getting to know the Rotobrush/Edge tool. It's pretty amazing. Not much more to say there. 

Now on the onset, I have two challenges that I could band-aid by using underlying masking to fix the issue, but I'd like to know how to fix them using tool adjustments first if possible.

1) I've got alpha/aliasing bleed (not sure what the real technical terme is) with my edge:

As you can see, the magenta is flooding into the man's hair. The edge looks great, not chewy at all. But the key is washing way far into the guy's hair/head. What do I need to do so I don't have track the edge with a core mask of sorts?

2) I can't show this without a video clip, but his blue/grey arm in front of a black/grey chair has a twitchy edge as the roto passes over. I imagine this is pretty common. What adjustment can be made to help calm down the rotobrush's edge interpretation/interpolation? I can go back. through it and even it out, but right now even s I do, it's twitchy like a lightning bolt.