Hi Imran,
I do not have the Corona Render here.
There is no option to integrate these in a selection.
I tried it with Fields and with CV-Parametrically selection. Placed it in the Connect and other merging options.
To get the result, I used the Formula Shader in the Layer mask. One time (01), the UV data was used, and the other time (02), the Y position was used.
https://www.amazon.com/clouddrive/share/CCiwln6oV55bIZORqH2bBEggnkd1b7Ndkek7Pt4DBVi
In Corona, you might use a Ramp/Gradient if the formula is not accepted.
All the best