Hello,

Right now as your Choix attribute has Image uploaded only, so to increase its Swatch size, you need to try out the following Custom CSS and paste it to Dashboard >> Theme Settings >> Custom CSS >> Global CSS section:

table.variations tr:last-child .cell [class*="wd-swatches"] {
    --wd-swatch-size: 4em !important;
}

.wd-swatch :is(img,picture) {
    object-fit: contain !important;
}

In this CSS, you can increase the value of the wd-swatch-size according to your choice.

On your other Site, there is only a Color Swatch being used as an Image Swatch and the size is already increased there.

Best Regards