^^Occam's razor says that you miscalculated
just kidding Totoro
i think your calculation show it is what it is, J-20 is longer legged than the F-22, by how much? 40%-50%? why not if it serves PLAAF's purposes
my take on this range issue is PLAAF needs a long legged aircraft, and they probably included it as a requirement to the J-20
PLAAF has not been investing heavily in tankers, and probably expect future engagement close to Chinese borders. This is a direct opposite of US global air power reach supported with many tanker fleets. For the US long range is preferable but not a main concern.
Thus without tankers, PLAAF expects aircrafts to rely own their own fuel load. And as PLAAF evolve the engagement periphery also changes. We now probably know where they draw the line, further and father beyond the Taiwan scenario, and PLAAF want J-20 to be able to reach there
probably in PLAAF book, J-20 is the main building block for Chinese air superiority in Western Pacific, and it will have to do so from the airbases in mainland