a lot of logia users power depends on the environment
imagine aoikiji fight ace on top of a volcano....i do say ace already won half a battle....now viseversa... ace fight aoikiji at the north pole....probably lose eh?
for luffy to defeat crocodile at his home field was very challenging. and the reason that crocodile was only 81 mil bounty is probably cuz he cant be too high to be appear so early in the seasons.. cant let luffy jump to 200mil in 3 arc..or 4? lol