I use the same ratio, and had the same issue. When I am cutting yardage I saturate with the starch and toss it in the dryer till it’s just damp, and then iron with medium setting. When starching blocks as I work, I press and then starch and wait a few seconds before pressing. The heat allows the starch to absorb faster IMHO.
Sadly I have been unable to find my beloved Niagra Starch in the non aresol bottle and have been using Sta-Flo.