Increase your spring rate at the rear of the car.
I usually use 10.0/12.0 in GT2
Then set your LSD with the front at 5/10/5
The rear at 10/30/10.
Drive the car. If the handling is better and it still understeers, start messing with ride height.
In general, if you lower the front/raise the back you get quicker turn in.
Remember, the setting are in millimetres. 25mm equals about 1 inch. So even if you have a difference that big between front and rear you only have an inch diff between front and rear ride height. You usually won't need that much. I usually start with a 10mm rake.
Hope that helps.