In my opinion, I think you should sit as low as possible for two reasons:
1) lower center of gravity (okay it's not that much)
The latter might sound ironic, but I think being able to look at the corner of your hood and the patch of road surface right in front of it is useless, let alone hindering your focus. If you keep your seat low and cover up the immediate front of your car with the dash, it may help you focus your vision far ahead rather than right in front of your hood, hence helping to you draw your lines better.
Try tilting the bottom of your seat back as much as you're comfortable with, and extend out the hamstring support. This will help you keep your body in place while hard braking, as well as cornering at some places.