I have all different sizes if you are talking about the plaited cross. The size I like best is 4" X 2 3/4", but I think I would like the arms of the cross just a bit smaller, so I'm still experimenting. But skyout's center in some form is the way to go. The traditional center is beautiful, of course, but does have back. The back side didn't really bother me until I made one that was the same all the way around.
Skyout, I can't do the cross like you do in roo, it won't hold. It has to be over something permanent.