Formulas: Reference parent item column from sub item formula column

Example:

WHEN {PARENTITEM_TRIP_TYPE_COL} = “MY_TYPE” ADD PARENTITEM_SUBITEM called “DINING RESERVATION” SET SUBITEM_DUE_DATE to 30 days before PARENTITEM_TRIP_START_TRAVEL_DATE

I have the formula to take date 1 and set date 2 30 days before date 1 within an item.

SUBTRACT_DAYS({Start Travel},30)

I see in the link at the bottom of this post that you can reference a parent_item in a query.

So it would be cool to at least say:
MY_VARIABLE = RESULTS OF QUERY(SUBITEMPARENT_COL2)

Then run the date setting function on the subitem date field like so:
SUBTRACT_DAYS(MY_VARIABLE,30)

Or in a less hacky way:
SUBTRACT_DAYS({PARENTITEM_COLUMN,30)

Thoughts?

Reference Link:

This would be helpful.
I especially need it to insert expiration dates in subitems based on the date of the parent item.
For example, the first subitem must be done 10 days before the parent item expires, the second 8 days before, etc.

Is it possible to flip this? I would like to reference a subitem in the parent item. Specifically, I have a list of tasks with dates, and I would like to have a column in the parent item that shows the “next” date in the subtask list.