When we moved here, we had a pretty good texture on the hard-surface floor so Yvaine and Merlin didn't slip, but I still set up some rubber-backed rugs where they often took turns at a run. When I asked them to practice sitting, they preferred to do it on the rug instead of the bare floor.
The kitchen has the best light, so when I started taking a lot of pictures of them sitting together, I started going there. The mat used to be facing the island, but it was easier to sit on than the floor, so it quickly became The Spot The Spaniels Sat.
When Baby Tristan learned to sit still, he sat on the kitchen mat because Yvaine did. It was automatic, enter the kitchen, go to the mat. If we practiced other tricks, we started from and returned to the mat.
And Gwyn... learned from Tristan.
I never specifically told them to sit there, but they seem to find it a comfortable, comforting routine.