I seem to remember that the Meade SN reduced it more or less by 1/2, for some reasonable definition of 1/2. Imagers seemed happy with it. I had a 10" which was very average optically, but the imager I sold it to was very satisfied.
-drl
If you place the corrector at the radius of curvature of the primary mirror then the coma is fully corrected but you have a tube that is twice as long. You also need a larger primary to have fully illuminated field. So you now have a Schmidt camera with a secondary in place of the film holder.
- Dave