I played a 4 knight game and when fighting Dragons, I would use a Windmaster, get the dragons in the air and then fly up under them until just their feet were visible at the very top of the screen. Then I would just flail away holding down the 'a' key. If I was positioned correctly the dragons couldn't hit me, but I seemed to do significant damage and could drop them quickly. Impossible to judge if I was doing the same damage I would have done if I'd been in the middle of their torso instead, but it seemed like it.
As Peter notes, I'm sure it's different if you're actually using the cursor to target a specific spot; I'm not sure how that all works out.