This is the response I got from Suunto Customer Support:
“This behavior is a known software quirk in Suunto’s Imperial unit logic rather than a defect with your individual watch. There is currently no setting on the watch or in the Suunto App to force decimal miles (such as 0.83 mi) below the 1-mile mark.”
“Why This Happens & Which Watches Are Affected
The “Sub-Mile” Conversion Logic: Suunto’s software designers modeled the Imperial unit display directly after the Metric system—just as Metric switches from meters (850 m) to kilometers at 1.00 km, Suunto’s Imperial logic defaults to displaying feet (0 to 5,279 ft) for any total distance, lap, or interval under 1 mile, only switching to decimal miles once you pass 5,280 ft (1.00 mi).
Affected Models: This behavior is specific to watches running Suunto’s newer UI architecture—most notably the Suunto Run (which runs a distinct, streamlined RTOS/Lite operating system compared to older models) as well as recent firmware builds on the Suunto Race, Race S, and Vertical. Legacy models (such as the Suunto 9 Peak Pro and earlier) displayed decimal miles from 0.00 mi upward, which is why long-time American users have frequently flagged this regression on the Suunto Community Forums.”
So that’s that! No way to change it, you just have to read 2,436 feet and try to estimate what that means.