I don't think social signals from those mostly empty social accounts are working at all - seems like other metrics are considered when determining whether the social signal from the account commands weight or not.
Accounts that have very high interaction or user input, are given heavier authority/weight when sending a social signal to your site, whereas, those accounts that have very little friends or rather 'empty' accounts, are quickly determined as the least priority given, thus they command very little weight when being used on your site.
Accounts with many friends or circles, very active, has high interaction - those would be good sources of social signals.