Confusing behavior of Descendants

I am trying to sum the remaining estimate of all linked tickets multiple layers down from a given ticket (e.g. a ticket has multiple epics, each containing stories that have estimates). The estimates may be split over different projects, and have multiple layers. I want to track the total estimate day by day to track total burndown.

It seems like Descendants are made to accomplish exactly this, with level set to Issue to get links all the way down, but I do not understand the output I get from this call. If I input,

SetToStr(
Descendants(
[Issue].CurrentHierarchyMember,
[Issue].[Issue]
)
)

and set a given ticket as Parent Link, I get all tickets in all the projects, regardless of linking. To debug, I tried instead to do

SetToStr(
Descendants(
[Issue].[Parent Link].[ABC-12],
[Issue].[Issue]
)
)

(ABC-18 is a placeholder name for a ticket in my Jira project). This returns an empty list instead. Is Descendants not the right call for this, or is my syntax lacking something?