Since are not graders and cannot side shift their blades the side to side elevated angles need not be too extreme since one track will be following the down side of the cut. To maintain the desired constant gradient the blade needs adjusted to a lessor cut angle frequently.
You will also find that shallower cut angles will have less of a tendency to cause the dozer to try and crab crawl due to the heavier loading on one side of the blade.
You may find that the 9° will be enough you could always knock out the seals later if need be
Have you given thought to whether or not you will have to stiffen the back of the blade or will the center pivot and a cylinder connected to each side of the arms be enough?