That's interesting, my serpaes have the opposite problem. They generally leave my German Blue Rams alone, and actually get chased off by my male if they get to close to the female, but they have been absolute bullies to my angel and I am considering trying to rehome him (or her) if they don't start asserting themselves more. The angel is relatively new to the tank so I think it's just territorial stuff going on with the serpaes and the angel being shy do to being in unfamiliar territory. I thought putting them in a larger school was supposed to help so I upped their school to 15 before I introduced the angel and they are still picking on them and nipping their fins. I wish I had some real advice for you but I can tell you that upping the number of the school does not always even out the aggression, in my case it's more like filling a playground full of adolescent boys lol. If someone else has more experience with keeping serpaes peaceful I would be interested to hear any advice also!
(Before anyone asks, it's a 46 gallon cube with a lot of plants and cover, with 15 serpaes, 2 GBR, and one medium Angel)