I think it takes in account how heavy is your foot, if you average 300 to 320 wh/mi the I think will give you about the 265 miles rated, however if you have a heavy foot then I think the rated range take that in account.
If you have an average of 400wh/mi then probably the rated range will be much lower on a full charge.
Most people don't reset the B odometer, if you didn't reset it, can you share what is your wh/mi average, may be that is the reason you are getting 236 rated instead 265 on a on a full charge.