I made a plate to cover the discharge today for mulching. It worked great. The problem is that all of the clippings/dust comes straight up on me. How could I fix this? I was thinking of making one out of expanded metal to increase the airflow out of the discharge but still chop leaves.

Do you have a mulching kit installed?? On my z-turn Gravely and John Deere mowers the mulching kits come with baffles that attach to the underside side of the mower deck and basically encircle the blades to help with the mulching and I do not have any dust or clippings coming up.

No. I threw this together. If I run over leaves without this they just fly out at warp speed no harm at all.

The expanded metal will probably just clog up after a few minutes run time, and then you are back where you started.

I run two Hustler Super Zs, one with a mulch kit and one with side discharge. The mulch kit unit blows a fine powder out the front anytime the grass and soil aren’t wet(which is a lot lately). That pressure has to escape somewhere. I’ve seen Dixie Choppers running the expanded metal chute blocker and they seem to work well enough. Those leaves are going to keep moving until they either drop out the back or are fine enough to blow through the mesh.

Do you have mulching blades on it?

No mulching blades

Thats the problem I'd say

Yup, regular blades are designed to lift, cut and sling it out .

Just the way it is