I have had my Clarity for a month (about 800 miles) now and it usually says 47 miles electric; 380 gas for a total of 427.
In an effort to understand how the 5 modes and the Econ, Sport, HV buttons really work (I originally thought they were like old radio physical detent push buttons!) I went into the thick online manual. There are good clues starting on page 11.
The interesting thing, however, is the description starts with the name: "Honda Sport Hybrid." Doing some research on the web I discovered that this is a somewhat different car sold in other countries such as Malaysia. There are good descriptions of its drive-train on the web.
My operative theory is that Honda developed and tested the drive-train technology on that car and then moved it over to the Clarity. In the process, they may not have changed some of the computer parameters which predict range for the evolved US model. This should be a simple software change (due to interactions, testing needs and deployment strategies, no software change is ever simple.) So, if Honda is listening, we may eventually see this mileage over-forecasting fixed in a future software update. Cheers,