The particles should have a velocity set under the Initial Conditions folder because after they travel a small distance and hit the plate, you want them to have a different velocity after making contact with the plate.

If you had a punch tool that was much stiffer/stronger than a soft material, you could use a velocity boundary condition on the punch tool to push it through the soft material.

I inserted your images below because ANSYS staff are not permitted to open attachments.  I haven't used the MASSALL() command, so I don't know what it does. Since the number is larger than the plate, does it include the mass of the particles?  What does workbench show as the total mass of the model?