Forget about grades. Terrible idea from the manufacturers. Concentrate instead on tone. Personally I split print with the hardest and softest filters. On my Saunders that is Magenta and Yellow just like on your color head. Don't mix the two. Just make two exposures, one through maximum Magenta and one through maximum Yellow. Usually it is best to start with the Yellow and only look for the highlight tones you want. Once you get that dialed in, do the same with the Magenta to fill in the deeper tones. Usually everything will fall into place nicely. You can also do much more effective burning and dodging this way as well. When you mix both into one exposure you create consistency errors between the "grades". You end up trying to hit a moving target which is no fun. There are charts which are supposed to ameliorate this problem, but turning three dials to a specific number every time you want to change something is just no fun at all.