There is so much dis-information I don't even know where to begin. BLUF, you will never ever never see 315 with 20ATs again. That was likely a software config mismatch. 21s get 314 by EPA, the rest "The Dual-Motor and 21" wheel combination is the most efficient, with the 20” and 22” wheels having a range reduction of 10-15% and 5-10% respectively. Estimates will vary depending on driving style and conditions.³" max you'll see with 20s at 100% is usually about 30mi less.
With 20s Ive averaged about 282 at 100%. That's pretty consistent since new 5months ago. You can get more than 282 in actuality, but 282 is average max imo. Driving habits, conditions, modes, suspension, all matter.
As for put it in percentage not miles, forget it. Just keep it in miles. Been Tesla since 2016, the S is kept in range left not percentage.