i dun know y also,mayb it's the weight or even the cut-out on the carbon fibre lower deck which affect the wind below the chassis,but the carbon reinforced lower deck does handles better than the carbon fibre lower deck.
i tried flexing both the lower decks,it seems tat the carbon reinforced lower deck flex more,and this might have help in the car's handling as the car would have more chassis flex which will improve handling...
anyway,the 04r is definitely a great car 2 have!!!...