Actually you‘ll get much better results for sympathetic resonance by using a convolution reverb with an impulse response of all strings resonating than by modelling the harmonics like this.
True story, I got that in a new Kontakt instrument coming up. The LivingRoom Upright Piano uses it for both pedal action controlled string resonances and body resonances, separately controllable. Not sure if it is more efficient too cpu-wise, but definitely more realistic and easy to make custom presets with multiple IR-samples depending on your preference. Also entirely based of the actual piano acoustics.