I agree that when a “block” is needed the amount of negativepoints are often more then i would like to place. On the otherhand it is detailed positioning what helps to outline a border.
What is helping at this moment is the opacity slider.
The controlpoint has a pupil, the small circlepoint which select the colorgroup and placing it on two colors halfway will select both. The threeparts of a cirlce, “iris” i am always thinking that it is apart of selecting the feathering, larger group of pixels which count not 100% but less for the selection. And the eyeball, the circle of influence. (which is for most new users a enigma because the effect is far more out of the circle then suspected and “m” showmask is your friend.) which is visible is that when the circle is larger the feathering, fading out of the white mask of influence, is smoother.
But the larger “eye” circle is invading parts in the image you would like to have not touched.
Your suggested brush and or eraser can help with that but the opacity slider in Local Adjustment tool can helpout.
1 larger (eye)circle thus larger more faded area of influence and smaller circle is a more hars edge of influence…
2 turn down opacity slider to turn down effect which helps to get that blend in effect, and by pushing the circle smaller you intense the adjustingeffect which levels the turned down opacity back to desired point.
3 alt click the last places it still touched undesired.
It hasn’t a multistroke eraser like the other maskingtools to blend in the adjustment.
The use of the opacityslider is a workaround but i like (it’s my favorite local adjustment tool ) controlpoints sins i understand how it works…
(and grouping controlpoints in smaller circles to somewhat influence the shape of the mask does help also…)