So looking at celestronaux.cpp,

bool CelestronAUX::slewTo(INDI_HO_AXIS axis, uint32_t steps, bool fast)
    // Stop first.
    trackByRate(axis, 0);
    AUXCommand command(fast ? MC_GOTO_FAST : MC_GOTO_SLOW, APP, axis == AXIS_AZ ? AZM : ALT);
    m_AxisStatus[axis] = SLEWING;
    command.setData(steps, 3);
    return true;
the aux command really is in 'steps'. So the hand-controller or indi-driver really does have to be smarter than the mount. The mount does not seem to know anything beyond encoder value.
So, my revised expectation is
1. Kstars says to the controller 'goto RA2, DEC2'.
2. The controller knows it is at RA1, DEC1 so, to go to RA2 DEC2 it computes the delta-RA and delta-DEC to get to RA2,DEC2.
3. The controller knows the mount's, encoder-steps per dergree so it commands the mount, thru aux command, to rotate RA by delta-RA-encoder-steps and delta-DEC-encoder steps.