The middle ones look the best as far as red is concerned, and by the looks of it, you just added one extra drop as the patches went to the right 12 total.
Right?
Tyson
I'm pretty confident that 50/50 will make orange. I say use the drop method, then scale it up for what you need in the ink cartridge.
One way to do this would be to use 1 drop Y to 10 drops M (10%) mix it and see what you think. Not good enough? Increase the Y to 2 or 3.
When you get something...
You could just use the Red ink from the i9900, much easier then mixing!
If you're intent on mixing, just document it and try all base percentages, 10% first, then 20% trying the batch till you get what you want.
Tyson