I understand what you are saying, though I would note that if a character is flat out sprinting, it is likely not Dodging. To full out sprint, you need to go roughly in a straight line, and so you don't have much extra time to dodge out of the way.
You can see the difference in a rugby or American football game. The ball carrier who is dodging and breaking tackles and trying to find a hole in the defense is not yet bringing the ball up the field at maximum speed. In a case like that, the running back is probably moving at say 2x pace and spending the other 2 AP for the round on a partial Dodge.
To fully and completely dodge with the maximum flexibility, a character would have to be mostly stationary. Take for example the case of the guys who catch arrows shot from bows: they're not running. They are mostly standing still and doing a full dodge.
So, that's how I rationalize it.
Now, some of us did consider houseruling a DB bonus for character movement because just plain movement, even in a straight line, does make a target harder to hit; that is just an empirical truth. So, you could give an additonal, universal DB bonus of say +1/10' of movement as a houserule if you wanted to reflect that.