When I read your earlier thread, I thought you had a Classic Turret. So, just to be sure, is the base of your press made of cast iron or aluminum? Is the base flat, or kind of pyramid-like?
If I have problems with primers dropping on the floor, I spread a dropcloth. Which is not a bad idea in any event. Powder spills and the detritus of spent primers are easy to keep corralled, too.
Cloth is better than plastic because of less static (which can cause spilled powder to scatter) and is less noisy and does not let primers roll around so much.
The Classic Turret (as well as the Classic Cast) drops primers down the center tube of the ram most reliably when the priming arm is in place. Without the priming arm in place, they spent primers hardly behave well at all.
Lost Sheep