P: Amount or Opacity slider for individual tools within a mask

Lightroom's new masking panel is very versatile, but I needed several times to control the amount of effect of an individual tool within a mask. This often happens in high contrast scenes, especially clouds that are brighter than the rest, or any areas that have different levels of brightness, like when the sun shines onto only part of a mountain or a valley.

Typically, in Photoshop, when applying an effect or adjustment as a new layer, we can easily control the extent of that adjustment by simply adjusting the opacity of that layer.

In Lightroom, although a mask does have an amount slider for the overall effect of the tools (linear or radial gradient, color range, select sky, etc.) that are part of it, there is no such slider available for the individual tools.

The Brush tool may be the sole exception to this rule, since you can actually control the extent of the effect of the brush within a mask, by adjusting the Density or the Flow sliders, depending on the situation. 

However, for the rest of the masking tools, this is not the case. It is especially important when using Add, Subtract or Intersect on a mask, because we may need to subtract part of the effect, not the full extent of it.

Here's a step by step example. 

In this first screenshot above, I have a partially retouched image where the sky needs brightening up. To do this, I add a Select Sky mask to bring it to the desired brightness levels:

With the sky brightened up, that big cloud is now too bright. To fix this, I subtract from the sky mask, using a radial filter:

Since the radial filter subtracts the entire effect of sky brightening, now the cloud is back to the original brightness which no longer matches the rest of the sky.

Ideally, at this point, I would have liked to have an opacity amount for the subtracted radial filter, so I can subtract only about 1/3 of the added brightness to the sky.

Here's a mockup as an idea, where we assume that an opacity of 100 on a subtracted tool hides the effect entirely (as it does now):

But, since no such slider exists, I am stuck to creating a new mask, copying and pasting the radial filter into the new mask (which by the way is not possible without first adding some kind of tool in the new mask and then deleting it after pasting) and countering the effect of the sky brightness radial filter subtraction by increasing exposure in the new mask, to bring the cloud brightness more in line with the rest of the sky.

This is a few unnecessary extra steps, if you ask me. 

So, what do you think about having an Opacity slider available for individual tools within a mask?