In the administration or in the form editor it is possible to make adjustments for attributes. The set of customizations is determined by the tl:TargetType. Currently it is not possible to distinguish between a composition and a general reference.
Certain customizations make sense to configure for a composition represented as a table, but do not make sense for references in general. For example, the possibility to define non-editable columns or whether new rows can be created or deleted in the table.
Create a composition and a "normal" reference. In the composition you should be able to configure e.g. "Not editable columns" as a customization. Not in the reference.