Help with a Paracorr Type 1

[RichardHurst]

Hi, I have recently purchase a Orion Optics 14 12" F/4 which has come with an off axis guider and a Paracorr Type 1. I wish to use this with my QHY268c 26mp APS-C Astro Cam. I am struggling getting sharp stars to the edges and wondered if there was a required spacing between the rear of the Paracorr and the Camera sensor. I'm used to using a refractor so this is throwing me a bit.