I think you could safely jump to 4u, Jen, if you want. If you are nervous about that, you could do what we call "fast-tracking." That means as long as your test results are still above 200, you can increase by 0.25u every 4th cycle. So 4 cycles at 2.5u then increase to 2.75u. That would help Rudy get into better numbers quickly.
In my opinion, I think fast-tracking is safe to do in your case - not everyone's, dear lurkers - because we already know that Rudy took 4u of ProZinc, and even with that was just in middle blue numbers. If you get a blue test, stop the fast-tracking strategy. It means you're getting closer to better numbers. At that point, you would slow down with the increases and revert to the normal guidelines. In your case, the SLGS guidelines, since he's eating dry food. Then doses are held for a week at a time.
This is just an option for you to consider. You don't have to do it, but if we'd given you advice on your starting dose, we'd have suggested 4u - this is just a choice for you.