The nozzle is based on Prusa R3 and Bear because they have the same physical dimensions from center to back of the extruder (23 mm). The coordinate system you see in image "ROB_Channel_middle.JPG" belongs to the simulation program and can be moved where I want. In the CAD model's assembly, the origin is located in the center of the extruder.
And according to my CAD files, the distance from Z0 up to the bottom of Prusa R3 duct is 3 mm. My duct is 1 mm higher than Prusa original and the distance from Z0 to the bottom of the duct is therefore only 2 mm.
And yes, we can try with your X_T Parasolid as a STEP file. But as I mentioned, I get many protests from the simulation. It is probably the conversion between several CAD formats that makes it happen.