"Horizontal tracking" means that the tracking axis is horizontal.  The tracking system adjusts the slope to maximize the solar radiation incident on the PV array.  So the surface will be inclined, but its angle of inclination (slope) will change in time.

To simulate a PV array with a horizontal north-south tracking axis, where the slope is continuously adjusted to track the sun, set the tracking system to "Horizontal Axis, continuous adjustment" and the azimuth to 90°.