Plinths for Monitor Audio Silver 8


I purchased a pair of Monitor Audio Silver 8's a couple of months ago and they sound great.
I have what is definitely a newbie question.
They came fitted with nice heavy metal plinths and then in separate boxes are two more plinths.
The ones on the speakers are flat and raise the speaker a couple of inches from the floor. The extra ones are slightly rounded and would seem to raise the speaker up just a bit more.
What is the reason for the two styles and how do you determine what is best for a particular use.
I am using the soft silicone feet on a hardwood floor.
Thanks
128x128granburyspring
Congrats on the 8s, amazing value. 

Did you buy buy them used? I ask because something isn’t right. They come with wooden plinths (in separate boxes), and screw in feet. That’s it. 

Btw the plinths are optional. MA says they don’t effect the sound. I don’t use them and I agree. 
Yes, I bought them used at a resale shop for $299. They were sitting in a corner gathering dust. 
I did get the separate boxes with 2 additional metal plinths in them with screw on spikes.
The speakers themselves are fitted with metal plinths on the soft silicone screw in feet.

They sound incredible as is. I was just curious as to why there were 2 sets. Perhaps the original owner had two sets of speakers at some point.