Many sanding discs are designed oversized to do just as you described.
If the disc were the same size as the pad or interface pad, when you either tilt too far or touch something with the spinning edge it would tend to cut into the wood causing damage.

Before posting here, I did exchange emails with the vendor.  I expected some explanation for the difference in sizes and discussion, more than most people don't have problems and I also sell 2" pads.  I don't want to keep an inventory of 2" pads and 2 3/8" pads, so if I have to switch to 2" for the radius pads I'll get 2" disks from Jon at our local woodturning group and stop using 2 3/8".

The radius firm pads from Vince are excellent for sanding the insides of bowls, and any concave surface. They work a lot better than the firm square edge pads. I have found that if I use a pad that is the exact same size as the disc, almost every time I will have 'mystery' scratches on the wood. I eventually figured out that these scratches came from the edge of the pad, and some times, especially when I was using thicker abrasive discs, the scratches would come from the disc as well. The idea of the over sized disc is to prevent this, and it does a good job. Since the disc is larger than the pad, when it goes over the edge, it has to flex, and that causes the creases. No problem with them other than on the coarse grit pads, some of the abrasive breaks off. If you have seen the wave discs that are scalloped on the edges, the cut outs pretty much match the creases.

I use 3 inch discs, well 3 3/8 from Vince, when ever I can fit it inside a bowl. It has over twice the surface area of a 2 3/8 inch disc, so more miles per disc, and less sanding time.

robo hippy