.2857 x 4 = 1.14 lbs of sugar
You have 1 cup of fat to 1.14 lbs of sugar, which is 2 cups fat to "about" 2 lbs sugar.
My recipe is about 1-1/3 cups fat to 2 lbs sugar.
Anytime I see a thread where the issue is "my icing isn't crusting well", 9 times out of 10, the recipe is a 1:1 fat/sugar ratio.
I'd reduce the fat to help it crust better, or add more sugar.