Nothing about 139.065mm nor about cameras with less than 55mm of sensor recess. Why would they not include the optimal spacing in the product description or specs? If you do not have the camera sensor exactly 139.065mm from the rear port of you C-925 what will be the effect on the image?
and as such, will not judge one way or the other. However, I have seen the official promotional material and specs for the CGX and best I can tell, Celestron makes no official claim for PE for the mount. It is possible that some mounts may have 5 to 10" of PE and others ...