So I just found this on BMW's U.S. website. Although it doesn't seem to match the i4 models here, it does seem to give a decided edge to the smaller 18" wheels. I might have to rethink wheel size.
Estimated electric range:
BMW iX xDrive50:
20" wheel: 325 miles
21" wheel: 275 miles
22" wheel: 300 miles
BMW i4 eDrive50:
18” wheel: 300 mi
19" wheel: 275 mi
BMW i4 M50:
19" wheel: 270 miles
20" wheel: 220 miles