Power window mask transparency/opacity question

I have an issue with not being able to control the opacity of power masks. Here is the problem:

I have a landscape shot with drone and I want to lift up the shadows of the terrain and leave the sky as is. I do a power mask with the gradient tool to lift up the shadows. Until here great but then I see that the untouched sky is too dark. Is it possible somewhere to alter the opacity of the mask. If I touch the opacity slider of the gradient power window it just lowers the shadow lifting of the terrain (all the node becomes grey) but I want the opposite -to control de opacity of the mask(the grey part make it more transparent or lighter)-the sky portion-

The only way I found is to duplicate the node and inverse the power window gradient tool and then I can control the opacity of the sky.

Would it not be much easier to be able to control in one node the opacity of the grey part of the mask and not only the transparent part? I hope I explained myself right.