Load your FBX into blender, convert it to Xps, load the created xps into blender. Assign your textures if necessary, adjust z axis of model into right position, scale it onto the floor size. Save it again as xps. Now your new xps should load in blender with the right proportions. bones+rigging if you have any, and the textures. now if your model is in the correct position in blender rotate it -90 on x axis and export it as collada. make sure to have a blender save point. Now import your newly created collada version into poser. This procedure will normally fix all the issues you encounter wit Fbx models. This method is used if you have a rigged model if it is not rigged you will need to export it as Obj and assign all the groups before doing so this way you can spawn all the groups in poser in a easy way to make a new rig.