River roach are turned on by the taste of fishmeal, and my local River Severn is turning up increasing number of specimen redfins on pellet baits intended for barbel.
These being hard baits, roach do tend to spit them out, giving fast unhittable bites. A partial solution is to use the softest hooker pellets that you can. I pump my own, which tend to be softer than pre-prepared baits. A 6mm pellet on a size 16 hook is about right. Try adding sweet strawberry and pineapple flavourings to hooker pellets.