I think is correct.
You must not multiply with rigid stiffness !
How you do your FE-Model (Vessel length bode site from the nozzle ?)
The best stiffness model in Caesar you become with additional rigid in vessel length with the same length as you have in your Fe-Model from nozzle centerline until your FE-Restraint.
With the force /moments result from Caesar back in your Fe-Model to calculat the stress.