Stranded - new Tesla 10 days old

[Veggen]

You're fortunate to have 243 V at home. Many people find their voltage drops into the high 230's when charging. It's the difference of a fraction of a kW that is giving you 31 miles rather than 29 which is the usual at 240V, or 28 if it's a little less than 240. The charger has a 10 kW limit-- the limit is kW, not miles of range.

Strictly speaking, the limit is the amps you are allowed to draw, so with a high voltage you get higher kW and hence higher mi/hr as the OP has discovered.