Appropriate parcel size is determined by the product own dimensions:

If the parcel has dimensions 20x20x20cm, then it is considered as size M according to the table below:

Plugin always tries to rotate parcel to make sure it fits the smallest possible locker.

Plugin always treats each product in cart separately. For example the plugin is not able to combine 2 parcels with size XS (5x30x30cm) to end up with locker size M. See the "Per Order" and "Per item" calculation methods for more information.

If there are no defined dimensions on the product, then it is considered to fit the smallest possible locker size. In this case size XS.