Also, how is the REAL_PWR parameter calculated? The calculation step given in the wiki seems to indicate that longer buffers will lead to larger powers, and also the units would become sqrt(W). :

This node provides the real power (as opposed to apparent power) measured during the last sample. The real power is calculated by multiplying every value in the channel 1 buffer by its counterpart in the channel 2 buffer, summing those results and square rooting the sum.