Mean for all features, not just one (Arcade)

[JoeBorgione]

I have a polygon feature class representing Meals on Wheels data by month/zipcode: imagine a 'stacked' set of polygons.  When I identify a given zipcode polygon, the pop up returns 12 values (one per month).  That's fine but I'd like to show the mean of all 12 months.

Using the Arcade mean(function) as shown in my screen capture below, I just return the mean for at given month, which of course is the same as the count.  How do I get the mean for all polygons?

[JoeBorgione]

Added moment later....

If I use the mean($layer, <field_name>) approach described here 

https://developers.arcgis.com/arcade/guide/types/#featureset

it seems to give me what I want: