Walk Behind Lawn Mowers

I just purchased a new HU775H walk behind mower. It fired up very well and runs nicely. My big problem is the buildup of grass under the deck in the rear near the bagger shoot. My lawn was not tall or wet at all. I was cutting on a taller setting too. I can't stand the clumps that are left behind every time you make a turn at the end of a row. Upon looking underneath, it appears that the plastic shoot filler is just too small and leaves a void where finely chopped grass collects. Is there any fix that is planned to make that plastic insert fill the space properly. Maybe I am spoiled with my old John Deere, but if this can't be resolved, this baby is going back after one cut. I would even be willing to pay for the part to correct this.