Best reducer/flattener for Vixen ED 103s

I am trying to determine the best match for a flattener/reducer for the Vixen ED 103s (current model apo doublet) that will optimize for terrestrial photography with an APS DSLR sensor. I want high quality (flat, sharp, color-free) over at least 90 pecent of the sensor field. The Vixen accessory 0.67x optic seems like it would be a good match, but I would prefer less drastic reduction in focal length. The Televue RF options at 0.8x seem like they might work well, but there are apparently two models designed for two focal length ranges, and the 103's 795mm FL falls in the hole between these two ranges. I also note that WO has just introduced a new 0.8x RF optic but it is optimized for smaller dia. objectives. Has anyone tested or reviewed a Vixen 103/TV reducer/flattener or any other promising combination?