Unable to change the sample pixel size for Emoji Color font asset

I’ve created a emoji Color font asset by using Noto Emoji font (font reference : GitHub - googlefonts/noto-emoji: Noto Emoji fonts). It creates the font atlas with the default settings. But I want to reduce the font atlas size by reducing the sampling point size. I am not able change that value modifying the sampling point size, applying settings reverts the sampling size to its original value.

Has any one faced this issue? Is there a solution for this?