Open the model in MED and look #1 for single vertices under the model itself, #2 look for the origin whether it is within the range of the models polygons, #3 compare the size of the model to the 'cross' of the origin in MED and compare that to the size of models which come with 3DGS.

I use models with the size of double or forth of the length of an edge of the 'cross', and I place it, that the cross/origin is in the middle of the model.

You can adjust the bounding box or whatever it is called with 'c_setminmax'.