Maybe - MAYBE - adding just a little rubbing alcohol would help the soap cut into the aphids.
I was thinking just yesterday that the next time one of my bushes is infested, I should spray half of it with one combination of soap and alcohol, the other half with a different mix. See which one works better.
I've read that "soap" is better to use than "detergent", because the fatty acids in true soap are what bothers the insects. I don't know if that's true, I only know what I've read.
