Custom goal to snap beyond a collision particle

Hi.

I have a simple problem that I can't seem to get to work. I need 2 points to maintain a minimum distance from each other, and move only on the Y-axis. One point should be fixed and one point can move.
However, the trick is: if the floating point is within the critical distance to the fixed point, it should always move down, beyond the fixed point and then aim for the minimum clearance. <edit> See the illustration below.
The last part, I cannot figure out, even with a custom goal.

Any suggestions?