Your Polish roo is being picked on because he's different and also because roosters very often allow the picking to happen without protesting. Your polish hen may object when the pickers focus on her, but she's also vulnerable because she and the roo are in the minority.
What would really help is for you to observe your flock to see which chickens are the culprits. You need to see what time of the day this is happening.You can learn a lot by simply watching your chickens.
I've been making a study of feather picking for well over six years. One thing I can tell you after all this time is that people like to offer a solution to a problem even though they have no personal experience with it, and they will repeat what they have read : "Lack of protein in the diet is the main cause of feather picking." If enough people repeat it, it must be true, but I've seen zero evidence for this.
What I have observed is that most feather picking occurs out of boredom and habit and it can start up when a chicken notices something just a little different about one of her flock mates, such a beard and muffs on an EE or the flamboyant crest on a Polish or a Cream Legbar. Once one hen begins to pick, others may notice and join in. You won't usually notice this is going on until it's noticeable that feathers are going missing. By then it's become a habit and it's very, very hard to break a habit once chickens get it.
One thing you can try is to set up diversions so that a victim will appear to stand out less. What would happen if you got several cheap feather dusters from a discount store and hung them around your run? If you have a lot of something that was originally unique, it will become less so, and chickens may lose interest in the feathers on the Polish or the EE. It's something I would try.
Another thing you can try is pinless peepers once you've identified the perpetrator(s). I've had pretty decent success with them, although a feather picker may learn to pick feathers again after wearing them for awhile. Nothing is a 100% cure for feather picking, and some pickers' brains are simply wired for it, and then there's nothing you can do to stop them beyond culling or segregating.
So, begin by observing your flock to see exactly what's going on, then take it from there.