Like you say, it is because they are drying out. The reason for this is because of the wind passing over your eye. Wraparound glasses will significantly help this (it is pretty much the only complete solution). I talked to my optician about this exact problem and that was the only thing that she could suggest. I don't know if switching lense manufactures will really make any sort of difference.
As for fit, the optician said that even if she changed the dimentions by a whole unit, I would wind up with the same size lenses because they are designed to sort of suck onto your eye.
What I can suggest is that whenever it feels like it is going to fall out (you see blurry a bit), stop and blink a few times till it becomes clear and/or put some eye drops in. I have found that they eyedrops keep the lense moisturized, but do not necessarily prevent it from falling out (though if it does, it takes long).