You'll need to put more recline in the seat. Just sitting on the floor board wont get you to the right place.

I have a Kirkey Intermediate seat I bought off a Spec Miata racer. The rear is bolted thru the floor with the humps cut out. Car is fine for me (6ft) with more recline than the seats 20 degrees. I did need to extend the steering column a few inches for this to work well.

My seat is at a 30 degree recline.