A CT on the incoming supply to the house (HOUSE SUPPLY > CT > PV + LOADS > MP2 AC-In-1).
The grid reading on the GUI has always been correct using this method and this is confirmed using a 3rd party energy meter (the type that counts the LED flashes on the utility meter).
What was incorrect however was the grid value shown in the VRM. It shows a negative grid value equal to the PV generation (when ESS is enabled and real grid power is zero). I started another thread for this issue but as it turns out, both issues were related to the setting for the position of the PV inverter.
With “PV on the output of this phase”, everything works correctly. It’s as though the system is not taking into account the setting for the position of the AC loads. If they’re also set to “AC input only”, the system should know that the PV is supplementing the loads and so the calculation for AC loads should be the sum of all three generators (Grid + PV + Inverter)