Try it on concrete--keeping in mind--even a slight excess might burn the grass. Watch carefully as the cement dries. If you use a flat fan nozzle and wave left and right...you must stop at the far right before you can reverse and come back left. This leaves an excess where you stopped. Just like spray painting--inexperienced painters leave an excess as they reverse the gun and paint drips occur at each edge. If you accidentally leave the flat fan at an angle as it moves back and forth...it gets worse. Surely you don't mean "flat fan" tip; those are designed to apply bands of herbicide over row crops, sharp cutoff, and not overlap at all. Tapered fan is more likely for boom sprayers--this allows the edges of the pattern to overlap the next nozzle...full coverage results, as the boom moves forward.
If you can apply the product evenly--whatever you do is fine. Just like varnish.