The AP reducer is supposed to be very good. There is a larger reducer they make too that also is supposed to work well, which is called an AP2.7 from memory. I used a Takahashi flattener on my RC8 when I had that and that worked well too.
I am currently using an TS Optical 3" on my RC12 which I have just about sorted out the back focus distance. However they do make a smaller version in 2" that might suit your needs and budget.
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