Questions as to picking colors for Hue Curves and Qualifier

When selecting a color with the qualifier dropper what color is actually selected? and is this consistent regardless of color space? or is it dependent on color space (timeline color space?) I am dealing with the Hue vs curves here but also wonder about the qualifier section.

I have noticed that when selecting a color for Hue vs. X with the dropper that the point given on the curve seems different and unexpected from what I have picked. For example: using an image of the generated color bars (assuming the these are rec709 primary and secondary colors as they do hit all the correct boxes on the vectorscope) When I select each with the dropper the point produced on the Hue vs curves differ from if I select the color buttons under the curve.

What are the actual Hues along the horizontal axis of the Hue vs curves? Are these calibrated to be something particular? and is the change in hue linear along the axis?

When I have a particular hue that needs to be changed I have a concern of the correct apex and symmetry or asymmetry of a bell curve on the Hue vs curves.

For a big picture question: Would there be a difference and if so which would be better for color matching camera and lenses off of a color chart - color wheels or curves or Hue vs curves?

Thanks.
Resolve Studio version 15.1.2.008

When I select each with the dropper the point produced on the Hue vs curves differ from if I select the color buttons under the curve.

I'm not seeing how this is a 'problem'. The colors under the curve are sort of...presets. If the preset doesn't fit the need, use a custom selection.

It's always thus with presets.