I've received a number of upgrades to J on the Embraer due to weight in balance issues. The last flight two of us were moved from 12A/C to 2DF. The flight was pretty full, but J still ended up with some empty seats. Not that I'm complaining, but anyone have any details on the algorithm? I've flown on the CRAs a number of times with almost empty J cabins and no re balancing.