I don’t like the gain optimization scripts at all.
I’d recommend reading the first two posts of this thread.
As you can see if you read more of the thread there are of course more opinions but the first two posts is how i would recommend to adjust gain.
Also it looks like you used the wrong gain optimization script because the numbers should change much more over that range of gain.
When changing the gain make sure you use the correct method depending on your system.
(For Beginners - How to Set / Change Gain)