I have driven about 10,000 miles on iX. Whenever you are charging it always takes you close to 260 miles with 80% battery. However whenever you start driving you won't get actual given miles for long or short trips.
For example, if you drive actual 20 miles, range probably dropped 25-30 miles. I get that it is because of climate/heating. But after 10K miles and adjusting to weather conditions that it is cold these days, BMW computer algorithm should give quite accurate mile range, considering if you are driving on the same route mostly.