3 phase power watts
V1 usually designates a Y-voltage, and V12 a delta-voltage. It seems, that you are measuring delta voltage acording to the value of 400. So the apparent power calculation would be correct with the sqrt(3) factor.
For the real power measurement, you must use Y-voltages, cause current and voltages have to be in-phase. Or you have to perform a delta-Y transform before multiply. I don't know, what you have actually been summing in your example for the real power measurement, but it don't work with delta voltages.