The display of variants within product sliders - if assigned via dynamic product groups - is based on the configuration from the storefront presentation. Even if individual variant options are explicitly assigned to the dynamic product group, it is still possible that the main product or a different variant will be displayed, unless it has been specified that the variants should be fanned out.

If I want to ensure that only certain variants are displayed in a product slider, the individual variants must currently be manually assigned to the product slider. This is because changes to the storefront display always have a direct effect on the listing at the same time, even though this may not be desired and the configuration should only relate to the slider.