Strange Behavior with Added Drives?

We've got a new 8202/720 that originally came with 6 drives that I formatted to Raid 6. System's been up and running but not in production for over a month. I decided to add another 2 to fill out the cabinet before the unit was placed into production.

When the drives were to the system and then to the Protection Pool, they show up with a different capacity than the original 6:

Size % I/O Request Read Write Read Unit Type (M) Used Rqs Size (K) Rqs Rqs (K)
1 198C 93046 15.2 .0 .0 .0 .0 .0
2 198C 93046 15.2 .0 .0 .0 .0 .0
3 198C 93046 15.2 .0 .0 .0 .0 .0
4 198C 93046 15.2 .0 .0 .0 .0 .0
5 198C 93046 15.2 .0 .0 .0 .0 .0
6 198C 93046 15.2 .0 .0 .0 .0 .0
7 198C 139569 15.2 .0 .0 .0 .0 .0
8 198C 139569 15.2 .0 .0 .0 .0 .0

Everything I've read so far just notes that Raid 6 effectively removes the capacity of 2 drives from the set, there's nothing that mentions behavior like the above with a quantity over 6. Does the sizes reported above make sense?

Bill