There’s no longer anything magic about the number 1480. It used to be the best approximation for 200 ms monitoring with an ATMega328P, but tweaks to speed up emonLib have made it wrong anyway. Until people say differently, we assume you’re using the emonTx/emonPi because most people here do.
All that I’d suggest is you try to make it sample for a whole number of mains cycles - if you can. You’ll minimise the “end effect” of including a part-cycle - and you don’t know where the cycle starts and ends, so the extra/missing part could be at peak amplitude or it could be around zero. That could well account for part of the variation from reading to reading that you’re seeing - just looking at those numbers, it’s about ±12%. I suggest you do as I wrote in another thread only a few minutes ago: 5 second intervals between EmonLib samples? - #4 by Robert.Wall