Pretty sure no one actually answered this question, so I'll take a whack at it.I don't know what the inefficinecy value/loss value is for electric Inserters. I just know that it has got to be lower than 2.13%.
Burner inserters have a listed 180 kW while running, and when taken through the formulas previously presented, gives a rough approximation of 8MJ of work done in 47 cycles. This is good enough for me to take that 180 kW figure as actual use rate. (Yes, I could go digging through files, but I'm trying not to, and just using math and observed values.
Electric inserters have a listed 13kW while running. But they also have a 50% efficiency penalty from the boilers, so to compare to the burner inserter, just double the use rate to 26kW. (It's probably 12.5 and 25, but let's let the rounding error stay and count it as a conservative figure.)
Now it becomes simple arithmetic. 26/180=x/.0213 or .0213(26/180)=x, x~= .003 or .3%
So yes, much lower inefficiency value in theory.
Easily proven with a similar setup you used to get the 47/coal figure, but having a pump, boiler and engine attached, and putting the coal in the boiler instead.
Factorio uses ideal networks and doesn't simulate heat or transmission losses.
My figure is likely a little bit off, since this method can't really account for the idle drain of electrical devices, but being that there's almost a magnitude of difference in power use, the power drain is negligible for all reasonable values.
And there's N9103's latest contribution to the science of Factorio