I started by running a discharge sequence on the charger on both packs separately, then connected them together and ran a charge/discharge/charge cycle. Now, they did get unplugged from each other and sat separately for about 3 weeks before I connected them to test in the plane.

Would one pack 'dump' faster than the other causing a big difference in the state of charge?

Not sure what you're asking with the forming question...one pack is a 8x8 cell brick and the second is just the 4 next to eachother (lengthwise). The combined 'pack' is just the 8x8 brick with the 4 cell pack sitting on top and velcro'd into place. The capacity is 3300mah.