Or how about try tweaking the angle at which the rack sticks out the back, i.e. tilt it forward a little, that could make all the difference. They're meant to be flat, but a few degrees won't hurt, provided you secure the attatchments in such a way that they won't slip forward on the rack. Also, use some bungee hooks diagonally across the panniers to compress that corner that's the problem, if you see what I mean, before you pack things in the bag....
What do you mean you have no bungee hooks?! (preemptive guessing game)
Or how about try tweaking the angle at which the rack sticks out the back, i.e. tilt it forward a little, that could make all the difference. They're meant to be flat, but a few degrees won't hurt, provided you secure the attatchments in such a way that they won't slip forward on the rack. Also, use some bungee hooks diagonally across the panniers to compress that corner that's the problem, if you see what I mean, before you pack things in the bag....
What do you mean you have no bungee hooks?! (preemptive guessing game)