If I understood correctly, I would say that the travel of the eyepiece holder tube, i.e. the focuser, is too short for the diverter (prism or mirror) not to be inserted. It is obvious that without a diverter, the focal plane remains very far out in relation to the extrusion of the eyepiece holder tube. I have the same problem with a Russian telescope. That is if I have not misunderstood.
Saluti
Giovanni
British Astronomical Association
Supporting amateur astronomers since 1890