I use the Sta-Flo also 50/50 or heavier if I need more stiffness. I also let it dry completely before pressing. I usually take my fabric right out of the dryer, spray pieces one at a time and lay flat around my sewing room til the next day, then iron. If I'm ironing something quickly, I do find it makes a bit of difference when you spray one side and press from the other side. I think it kind of draws the starch into the other side.
My mom was not a starcher and was struggling a little, so I asked her to try it on her last quilt...she's a definite convert!