M27 from Norway + a question

[oernulfs (Ørnulf)]

Approximately 2hrs 10minutes of 300s exposures through a Celestron 9,25 with a f6,3 reducer/flattener.

Camera: Atik 383L+ color camera.

Mount: eq8

Guiding: loadstar through a William Optics 90 mm.

Question: what is the proper distance from the camera chip to the reducer for Celestron's f6,3 reducer? I've seen numbers ranging fro 85mm to 105mm.

Thanks for looking.