IMO Scott has it all right. There is no tread on the tire, so it is not directional. Side bite or forward bite, unless (like Scott said) tire is beginning to roll over due to being too soft. Up untill that point, softer equals more grip in either direction.
I was shocked when I learned that tire manufacturers use a different type of rubber for front! I found out a few years ago and have been a bit miffed by this ever since. When questioned, they say it is so that the front tires wear longer!
I ask why should I want my front tires to last longer than the rear? This dilema is the reason we have to run harder rear tires! EVERY tc I have had, wears rear tires faster than front, requireing the use of firmer(and or larger) rear tires to keep car from pushing badly during last part of longer races.
I would prefer it if tire manufacturers would leave set-up choices to the racers, and produce tires with the same kind of rubber for both ends.