I have found that most of my chunking comes from how well the body is cut and mounted and how wide the rear of the car is. I noticed that at full width, 172 mm, the rear tires were almost even with the body. When I narrowed my rear axle I eliminated almost all my chunking problems. I don't know the offsets of those two tires you mentioned but the thought crossed my mind that the jacos might stick out a mm or two more than the parmas allowing the rear wheel cutout in the body to "sit" down on the tire in some situations cutting a chunk out of the foam.