I'm not sure I completely understand your question but one thing I have had to use recently is found here https://docs.intersystems.com/irislatest/csp/docbook/Doc.View.cls?KEY=D2MODEL_prop_for_list

I had a level which was a list and I too wanted to define properties for the level, the property would be for each element of the level/list.  In my case I defined my level to run off of an expression where my expression returned a list of values.  Then for my property definition, I used an expression as well.  In the expression, I called a method passing %value.  

Hope this gives you something to go on.