Boeing says this has to do with revised assumptions for pax, bags and seat weights. We don't know how Boeing revised those numbers, but as I wrote back then something did not add up from the beginning when comparing the range of the B737NG with the B737MAX.
With a range 4% shorter now for the B737MAX-8 than before the comparison to the old number for the B737NG would make sense, but the new range for the B737-800NG dropped by almost 5%. So it still does not make sense when directly comparing the numbers...
UPDATE: Aviation Week reports that the extra weight per pax/bags and seat is 15lbs. Let's have a look at some numbers:
- The B737MAX-7 "looses" 500nm with 126 pax and therefore a payload that is higher by 1890lbs than before (126pax*15lbs/pax).
- The B737MAX-8 "looses" only 145nm, although payload is higher by 2430lbs (162pax * 15lbs/pax)
- The MAX200 "looses" 645nm. Payload is higher by 3000lbs (200pax*15lbs/pax)
Comparing the -MAX8 and the -MAX200 us even more intriguing. It is almost the same aircraft, but the -MAX8 looses 0.06nm/lbs and the -MAX200 looses 0.215nm/lbs.
This looks weird to me and Boeing should explain these differences more in detail.