how do you use a parent field in child formula

Hello everyone,

I have two custom record types (CustomParent, CustomChild)  I have a field custrecord_type in the parent record type and I want to modify that parent field in a field on the child record type using a formula.  I passed the custrecord_type into a field on the child record using the source & filter section but since the field has to have the "store value" field unchecked in order to work the value doesn't show up for any formulas that reference it.

To be clear I'm not trying to change the value of the original parent record just make a extended version of the text field using CONCAT in the child field via a formula working on the sourced child field referencing the parent. Is there anyway to do this or am I looking at this problem from the wrong direction?