When you roll on shortening, the fondant tends to "hydroplane" along on top of the surface and settle back down in areas, trapping air. When it's "sealed" to a surface (without sticking), it doesn't float and lift and let anything under it. It's like tires on a wet road basically.
I will do my best to get to the kitchen I work out of today and get some measurements on the "mini" if I can not get info direct from Sweetwise.
As for the "sealing" of the fondant to the mat...you actually want this to occur but as I believe a poster had mentioned before; be careful not to go too thin as this can cause problems especially with getting it off of the mat in one piece....never measured how thick or thin I roll mine I just run my hand over it and can feel when I think it is right. Anyone having problems peeling it back off of the mat try rolling a little thicker and see if that helps.
Here is one of the videos................
They do tell you to use a different rolling technique and I think it works rather well. I also mentioned before that the surface actually let my (wooden) pin "glide" across rather then rolling. Kind of just happened by accident but once it did I did alot of the work just like that. It was quick and somewhat effortless! Mind you, this is a vintage pin possibly antique. I use it because it is so heavy.