I changed most of my Flyer style couplers to the scale sized ones. Since I run passenger trains as a unit, I don't care if the couplers uncouple or not. I've been able to bend the Delrin scale sized couplers quite a bit to correct any sag and align them better. The Flyer ones can also be bent along the arm to raise them. I've done it without breaking them. But then I also have a small bag with all sorts of AM couplers. American Models also has a few hints in their site(at least on their old site) that allows better performance.
Dont be too afraid of breaking the arm. The plastic is tough. Just try a little at a time.