There was a lot of incorrect items stated as fact in the quoted post.
1. The stock 20s and 21s do not have the same rubber. See below.
2. The size of the rim does not impact (much) the overall size of the rim/tire combo (i.e. there is no "bigger circle" except when moving from 19" to 20"+, and that difference is 0.6"), and therefore it does not impact range. As I mentioned above, range is impacted by the width of the tire because it has a larger contact patch as well as a composition of the tire… More sticky will have more rolling resistance and lower range.
19″ Aero Range – 245/45R19 Pirelli PZERO AS+
OVERALL DIAMETER: 27.7"
20″ Aero Lite – 245/40R20 (Front) / 265/40R20 (Rear) Michelin Pilot Sport EV.
FRONT OVERALL DIAMETER: 27.7"
REAR OVERALL DIAMETER: 28.3"
21″ Aero Blade & Sport – 245/35R21 (Front) / 265/35R21 (Rear) Pirelli PZERO PZ4
FRONT OVERALL DIAMETER: 27.8"
REAR OVERALL DIAMETER: 28.3"