The reason for the 1 L (1 US qt) sparge volume difference with the Grainfather app and G30 instructions, is that the basic formula printed in our instructions don't take into account if you are using a 220V or 110V version Grainfather.
Because the 110V heater version has less power capacity than the 220V version (1600W vs 2000W), the boil evaporation rate is less (2 L (2.1 US qt) per hour instead of 3 L (3.2 US qt) per hour).
So for a 60 minute boil, with the 110V unit you have to sparge with 1 L (1 US qt) less, because you lose 1 L (1 US qt) less during boil off.
For the more precise results, please see our calculators online or use the app.
The printed formula in the G30 instructions is to show you mostly, how the calculation works, however it will of course differ depending on which unit you have.