Thanks for troubleshooting, Kathy. I have one other envelope selected but it is too small for the package I am talking about. I have only selected two other packages: flat rate padded envelope and a flat rate medium box.
I was using my zip code but it shouldn't calculate regular priority because I don't have that package available. And when I increase the quantity to 5, for example, it should default to the medium flat rate box for $12.75. Instead it is quoting $17.