You can try another in. May have to go more than that. Keep lowering until it feels right. If not low enough, it can, and probably will kick you in the face. My Trap Special is about 1.250 lower. Your mileage may vary. Hope this helps, Roy
John, if you were comfortable with 1 1/4" drop at heel with your low rib, then just add to that the difference in height between the ribs. That will give you the same shoulder/rib relationship as before.
My comb is 1 1/4" lower than the rib, and both front and back are parallel with the rib. 1 1/2" is considered standard, but everyone's cheek structure is different. I've found that 1 1/2" drop tends to make my guns shoot too low.
As zzt noted, to maintain the same comb/rib relationship, you will need to raise the comb the same amount as you raised the rib. That is, if you raised the rib height 1/2 inch, you will need to raise the comb 1/2 inch to keep the relationship between your eye (rear sight) and the front bead (front sight) the same as it was before you added the rib.