Most of the combines I have seen with your tire configuration have the rear axle set at position n2. This raises the rear slightly higher than the front, maybe 1 to 1-1_2" higher in the rear. This is in addition to the natural uphill slant already built into the positioning of the sieves. You will be able to tell which hole you're in because the large cast-iron rear axle support that the bolts go through is numbered 1 through 4 on the BACK of the casting. Position n2 is where I would set it.