I've figured out the understeer issue with a bit of close analysing.
The game has a speed sensitivity type filter on, it limits how much steering angle it allows you to apply based on your speed and gear choice. After you hit the limit for your speed the game ignores further input and you can even feel this through the wheel's FFB and see it on screen (The wheel hits a sort of squidgy dead zone feeling), in order to then add more lock you have to slow down. As the speed decreases through a corner the ammount of steering angle available increases, in a low speed 1st gear corner the squidgy dead zone is completely gone because 100% steering angle is available.
It is a strange system but its liklely responsable for both the lack of typical dynamic oversteer effects and the understeer.