The way I read it, rank for fighter is "Kills per Death =
TotalKills / ((Discos * 0.5) + Bails + Captures + Deaths + 1)
"
(I may be wrong, but here is my take)
Some of your TotalKills may count in your K/D but not count towards rank.
When looking at your score, you can click on the "Kills" link and see there are some kills that do not count towards rank, I think you do get credit for them in the "kills per death" column. One way to get a kill that doesn't count towards rank is to send an M3 driver back to the tower while you are flying in fighter mode. You would need to be in attack mode to get the credit, but of course it will count towards the attack score. I am lead to believe this because of this statement under scores..
Only air categories are scored for fighter mission types , ground categories only for bomber mission types, and both air and ground are scored for attack, vehicle, boat and field gunner mission types.
If I am correct in my assumption, this may be why the higher K/D may have a lower (higher numbered) rank.
Disclaimer: I didn't stay at a holiday inn last night, so I may be WRONG!!!!