Consolidating data from two inputs for creating total KWh charts

So now that I’ve got a couple of days data into the system, I’d like to get some useful charts out of it.
At the moment, I’ve got CT inputs from my two fuseboxes, with a dashboard showing W graphs for each + the supply voltage (from virtual feeds that combine the two inputs).
Looking at the docs for creating daily charts

it’s leaving me a bit confused as where to make the calculations as that page seems to be describing a single feed, so logically I should be using the virtual feeds I’ve created (for total W and total Wh).
Except that doesn’t appear to be how it works…

Or should I just add a third CT clip on the input before the electric meter that should hopefully give me a real total?..