The rutile and cobalt are definitely helping the melt. They are quite smooth but still matt, 16 more than 17. I think there is too much glaze in the squares as my tiles of the glaze came out with a better melt and it's the same recipe.
Here is a comparison between tiles 16 and 17 50/50 soda feldspar and whiting, with the bottom row square 16 from just whiting flux. Need to keep looking around this area a bit more.