How to create a second instance that is only one strip for the bottom and not full length

[sperkowitz818]

Hope this is the right place to ask this. I have LEDs in the back of my TV running off one controller. I create another instance with another controller for one strip that is below my TV to light up inside a TV stand. The length of this strip is not the full length and is centered. I can't figure out how to change the length of the strip and make it centered and to only react to a video in that location. I was able to use 50% edge gap, but according to the colors it looks like the far left/right will still light up on the edges. Basically, it looks like all it did was shrink the strip but it still reacts to the entire length of a video. Maybe I'm wrong and what I have there does do what I am trying to do as I haven't had the opportunity to run a better test (it was hard to know for sure with a video I had on hand at the time). I am basing this off the color gradient.