There is often some confusion about the "rowing" of chopped leaves left behind the mower. This is typically an issue during the late fall's peak leaf drop accumulation. When you’re processing large piles and heavier volumes, such "rowing" can be expected, requiring a second pass. For greatest efficiency, keep pushing the processing into the pile of unprocessed, meaning in a clock-wise motion.
Take on no more than 2/3 or 3/4 of a deck's width of material at a time. With a full deck's width, you may be making the machine work too hard, often resulting in the “toss” of some un-chopped leaves right out the front and sides of the mower deck - it's simply a case of too many leaves at a time for the mower.
In every pass over the leaves, you want to strive to get the absolute perfect amount under the deck. No more-no less… It’s and experience thing. Your eyes and ears (mower engine sound) will tell you what you need to know.