Reduction factor from the SCT corrector much less than 0.77 - nearer 0.88.

[William Shaw]

I recently acquired the 0.77 SCT corrector via the second hand market. I know this is no longer sold but wonder if someone can help me. It is stated to have a 0.77 reduction factor, but when I fed this into my plate solving system (NINA+ASTAP) I got errors and the system eventually reported a rather longer effective focal length from my C8 SCT+ the Keller/ASA part. It corresponds to a reduction of around 0.88!

So I am curious to understand what might have happened. I had previously been using a Starizona corrector with a 0.71 factor and that was confirmed by the solver. I adjusted my Backfocus as carefully as I could to get the right spacing for the ASA part that I substituted. 

Is there another model of ASA corrector with a smaller reduction? Is the degree of reduction exceptionally sensitive to the distance to the sensor?