I love the SPS system for stacking but have one problem.

The cake sits on a thin cardboard cake board, and then that cardboard is placed on the SPS stacking plate.

When I stack the cakes the cake board and plastic plate are visible. I do push the plastic plate so that it is completely touching the top of the fondant lower tier below. But that darn space is still obvious.

Usually I cover with pearls or a ribbon as the cake design, but is there any way to use SPS if you do not want anything at the bottom of your cake tier?

You need to make sure you have 4" tiers. You can buy the longer legs and trim them if the tier is not 4".

My tier was exactly 4" tall and the SPS plate touched the fondant beneath it.

Sorry if I wasn't clear. I'm talking about the space created by the thickness of the SPS plate and the cardboard cake board.

I cover the cake so the fondant goes past the cake board, so it can't be seen. To cover the edge of the plastic plate, if I'm not doing ribbon or a RI border, I mash some fondant (same colour as the cake) to a very thick paste with water. Pipe this in the gap and smooth with the help of a damp, thin paintbrush and a small spatula. The water in the paste evaporates, so you get a seamless finish. It's the only think I can think of.

Or, sometimes if your tiers are ever-so-slightly higher than 4", your plastic plate/legs will sink more into the tier below when you place the cake on top, pushing it in a bit more, so your fondant on the top cake edge will meet the fondant on the bottom cake completely.

But try the trick with the fondant paste in a piping bag and smooth it out, it really works.