This is a trick I've used before, but I didn't realize potential until I started talking about it for someone else's benefit. This goes back to Whispies and Upping Opacity.
The problem? Nasty halo around and extraction job that is causing too much trouble. You would like to just contract the mask, but too much edge is lost. Tightening the mask looks just as nasty.
The solution? Modify the background immediately around the object/subject. Simple enough.
Okay, you've got your extraction with some halo.
Copy it and turn off the original job.
Tighten the mask ever so slightly to get rid of most, or all, of the halo.
Apply the tightened layer mask. Yes, I said apply it. Transparent pixels are needed.
Copy it and order it down.
Give the copy Gauss of around 1 - 2.
Copy the Gaussed copy and merge down (ctrl + e).
Copy and merge until you are happy.
You should end up with around a 4px border that matches the outline of the object/subject.
Go ahead and merge down the tightened copy onto the Gaussed/copied/merged layer.
Now load the original alpha mask with the halo, and apply to your bordered layer.
That should take care of most cases in a general, all-purpose manner.
Back to the salt mine.