prolems selecting sky in LR 6

I'm using LR 6 and am having problems properly selecting the sky in my pictures. I create a mask with density 100, flow 100, mask out the sky using auto-mask, then reduce the brightness of the sky or increase the blue saturation of the sky. Problem is that that the sky almost always includes tree branches and LR leaves a "border" of sorts around the tree branches - an area which is not selected. So when I make my adjustment, it leaves a hard edge along the tree branches. I've tried using feather of 0 and I've tried using larger values for feather, but I can never seem to get a selection that goes right up against the branches like I want.

The second, related, problem is that when I use auto-mask to select the sky, it often results in what is a sort of "spotty" mask (with the mask color enabled). That is, some of the pixels are not selected leaving a spotty or grainy mask. The only fix I have found is, after making my selection, zooming in to 100% and disabling auto-mask and re-masking the areas that are spotty until all pixels are masked properly.

I've been demo'ing Capture One after becoming disillusioned with the death of LR standalone and it doesn't seem to have this problem. It can also reduce highlights in an image (in this case, the sky) without affecting the rest of the image whereas reducing highlights in LR seems to affect the mid-tones some too. Maybe there's a way to do something like this in LR instead of masking the sky and trying to tweak it separately?

How do I fix these two problems?