Animations in Flexitive affect all sizes. This means that all sizes you activate in a particular page will have the same animation sequence.
If you want different sizes to have different animations, we recommend you duplicate the page and apply different animations in the duplicate. For more information, check out our articles on Duplicating a Design and Using an Existing Design as a Template.
While animations in Flexitive affect all sizes, changes that only affect one size will still be reflected when animated. For example, if you animate a hidden object, it will still be hidden. For more information, check out our article on What Changes Affect All Sizes vs One Size.