Theres a point on the Chinese coast 29.60miles (29d 04'51" N 130d 40'20.08" E ) near Shanghai that is exactly 530.95m to Fukuoka, so, if im reading this right, if Chinese planes took from somewhere around the point near Shanghai, they would be able to get to Fukuoka, and half way back before they need refuelling, but if they cut the Fukouka out and just bombed the crap out of nothing at Fukuo-jima, then they should be able to make it back to where they took off from, if not, then they could air-air refuel close to the Chinese coast. (theres a whole bunch of islands 78 miles closer to Japan then where they took off from...
Its possible.. that they were on purpose....but unlikely?