A little complicated to do an areodynamics course …
Control surfaces activated by hydraulic power return to servo command neutral point on ground and in flight , for others the control surface remains where the pedals are on ground and where the neutral is determined by trim due to aerodynamic forces on the control surface in flight.
Hydraulic controls have a speed-dependent force hardening system that has no effect on neutral position , only on effort to apply on pedals or control column .