The servomechanism does not influence turbine losses, but turbine performance as a function of servo-stroke is normally registered for turbines in operation and will give important information for modelling an existing turbine.
"Servomechanism" handles four types of mechanisms.

A fixed linear servomotor with cross-head connected to a rotating ring.
A tilting linear servomotor connected to a rotating ring.
Individual linear servomotors and a
servomotor connected to a ring with linear movement.

The servomechanism is exposed to  great forces depending on guidevane/turbine design and mode of operation.
Deformation due to these forces is not calculated, but a pre-stress related to stroke is taken into consideration. This will result in a constant stroke-displacement instead of a variable depending on forces. Guidevanes will stay closed for stroke less than the set pre-stress.

The default servomechanism displayed the first time window is opened has a tilting servomotor.

By the aid of a slider operation of servomechanism can be "tested".

Window shows servo mechanism design parameters for a Francis turbine type. Diagram; relation between stroke and time.