responsiveimages set multiplier based on (backendlayout) colpos and contentelement

How can I set the responsiveimages multiplier based on the colpos for a specific contentelement (carousel.text_and_image)?

I have tried this:
In the default backendlayout the colpos 8 should be modified.
```
lib.contentElement.settings.responsiveimages.backendlayout {
default{
8 {
contentelements {
carousel {
text_and_image {
multiplier {
default = 10
}
}
}
}
}
}
}
```

this works, but effects all carousel items:

```
lib.contentElement.settings.responsiveimages.contentelements {
carousel {
text_and_image {
multiplier {
default = 10
}
}
}
}
```