Tosca Test Case Design relationships with Classes

I am doing test case design on the Sample Application sampleapp.tricentis.com. I want to do the test design in the most re-useable way possible, so i have split it into classes.

I want to create a relationship to yield all instances of the Fuel Type and Mileage, however when i do this, it informs me that This is a class reference, you must resolve this reference. This runs contrary to my need to have a modular test design. I am unable to create relationships on the class level, so what is the best way to resolve this?