the mentioned formula works, but it may not show an immediate result. Maybe the parentRow is a bit slower than the thisTable or thisRow references we are used to. I would love to read some @Coda1 feedback in this regard,
It doesn’t look like this is possible when you create the template in a “true” page. But if you create the template in a canvas column page, you should be able to include formulas that include “thisRow.” And you can then reference this canvas column template in the “value for new rows” field of your canvas column settings.