22.3 Record Type and multipleDropDownField. How can the field hold an array of values without a CDT?

Trying out record centric design for the first time and I have a multiple dropdown field on the interface. Using the recordType (no data yet, just structure) as a rule input does not allow for me to specify a field as an array (like can be done with a CDT). Is there a way around this or is it as simple as 'if a multiDropdown is involved a CDT must be ctreated?