socommatthews,
Think about the procedure and you can fine tune your process. ONR has limitations. There is a certain level of dirt/soiling that is simply too much for the solution. But within those limits, you can move & tune the process as well.
Sheepskin is definitely recommended, because a high pile/nap mitt is more gentle and it is able to hide dirt particles between its fibers better. A dense, thick mitt can absorb & lift more water to the soiled area, which means more active ingredients to clean and more water to carry the dirt away. Using a relatively thin mitt or towel may reduce the overall effectivity of the process.
My recommendation: Mix up different strength ONR samples. Experience how these dilutions behave on your finish. Feel how the mitt glides over the surface. That would provide a nice comparative base for your mind/hand how the ONR should feel when you working with it. Next, try it on a lightly dirty car. Use the standard solution on it. Lift plenty of water from your bucket to the area you want to clean. The dilution of the ONR solution is correct when you see that the polymers are breaking up the water film immediately, and the mitt glides well, because the surface is slick. If you are unsatisfied with the slickness level, use more ONR.
I live in Hungary, and we have older cars which polluting more; spitting out a stubborn, disgusting fog. The resulting road film is very reluctant to remove and I have to use stronger mixes than the original, recommended one. I had to find the proper amounts and methods, but the results are well worth it.