Formulas for External Data Sources

Blown away by Skuid Connect and looking to take elements of it to the next level.

I want to create a UI-Only Formula Field that divides two numbers provided by a connected data source.  That said, when I try to do it, it doesn’t work. 
The fields in the model don’t show up in the formula builder, and they don’t show up when called upon by the {{}} or {{$}}.

Any ideas?