just bought a new snapper hivac self propeled mower last summer and notice alot of un cut grass when mulching even at the slowest pace, side discharge is perfect. why
had a ninja on it then put on a gator same results ,seems like the grass gets blown down away from the deck resulting in a poor cut,this happens in mulch mode only.
You need to make sure the front of the deck is approximately 1/4" lower than the rear of the deck if you can adjust it. That in addition to the proper blades and blade tip speed has alot to do with the aerodynamics of the deck and how it stands the grass up and cuts it evenly.