So I decided to try it again the other day and this time I happened to take the foot from a different accessory box rather than the box I've always used. I didn't even think about it making a difference, I just grabbed the one that was handy. And what can I say? Here it is, THE PERFECT HEM, done with the good old Singer narrow hemmer foot.
So how could I suddenly get this result after years of failed attempts? What did I do different? I didn't do anything different. But there is a difference. Look at these three feet - they are not exactly alike!