https://www.kitplanes.com/design-process-droops-and-vgs/

...Vortex generators used to increase maximum lift are not placed at the extreme leading edge of the wing, but they are usually well forward of 25% chord. The proper position is a compromise between maximum lift and cruise drag. Moving the VGs forward increases maximum lift, but also increases cruise drag. The optimum VG position is the farthest aft location that produces the needed improvement in stall characteristics...

...An important exception to this is if the wing has an airfoil designed to have significant laminar flow. The vortex generators will trip the boundary layer from laminar to turbulent, and no laminar flow will exist aft of the vortex generators. This is important because in order to significantly delay the stall, the vortex generators must be well forward on the wing while a good low-drag laminar flow airfoil will be designed to have laminar flow to at least 40% to 50% of the chord. The vortex generators will trip that flow well forward of that and dramatically reduce the amount of laminar flow on the wing. If this happens the drag penalty of the vortex generator installation will be quite large because the loss of laminar flow will increase the drag of the wing itself quite significantly.