Perhaps the IPID will solve this mystery:

 # hping2 -i 1 -p 113 -S 216.163.140.226
HPING 216.163.140.226 (eth0 216.163.140.226): S set, 40 headers + 0 data bytes
46 bytes from 216.163.140.226: flags=RA seq=0 ttl=48 id=4793 rtt=74.6 ms
46 bytes from 216.163.140.226: flags=RA seq=1 ttl=48 id=57960 rtt=74.7 ms
46 bytes from 216.163.140.226: flags=RA seq=2 ttl=48 id=9456 rtt=74.7 ms
46 bytes from 216.163.140.226: flags=RA seq=3 ttl=48 id=30735 rtt=74.6 ms
46 bytes from 216.163.140.226: flags=RA seq=4 ttl=48 id=29779 rtt=74.8 ms
46 bytes from 216.163.140.226: flags=RA seq=5 ttl=48 id=18545 rtt=74.7 ms
46 bytes from 216.163.140.226: flags=RA seq=6 ttl=48 id=57474 rtt=74.7 ms

 # hping2 -i 1 -p 113 -S 216.163.140.227
HPING 216.163.140.227 (eth0 216.163.140.227): S set, 40 headers + 0 data bytes
46 bytes from 216.163.140.227: flags=RA seq=0 ttl=48 id=53009 rtt=75.0 ms
46 bytes from 216.163.140.227: flags=RA seq=1 ttl=48 id=30087 rtt=74.7 ms
46 bytes from 216.163.140.227: flags=RA seq=2 ttl=48 id=63243 rtt=74.6 ms
46 bytes from 216.163.140.227: flags=RA seq=3 ttl=48 id=36291 rtt=74.6 ms