It’s a “WTH”…
Why the heck is it so hard to find the base sensor some template(-like) sensor is connected to? It should be one of the columns of every list containing synthetic data.
In my own case: Please add an additional column to the table displaying all helpers (http://ha/config/helpers) showing the input sensor the helper is based on. This should probably be done for every kind of template sensor.
I messed up my energy monitoring because of literally hundreds of sensors coming from my zoo of intelligent (ROFL) power meters… Debugging that took hours and I got flat fingers from all the clicking.