Sounds like this is really a tuning question. Center shot or not (and my AMF model is), if you're shooting off the shelf I've found putting a little bump (like a matchstick) under the rug & side plate makes less arrow contact and better fletching clearance. I don't know about a feather rest, but if you have to build it out to get better arrow flight (to "bend around the riser") you shafts may be too weak.
Since you are shooting a bow that is 6" longer, brace height is probably different, which will change things.