Hi PK,
You might need to explore 'Push Distribution rules' for surplus supply situations.
Fair share rules might be triggered by deployment only if 'demand exceeds supply'. In situations where supply is sufficient to cover the demand, or surplus, Push rules would be applicable.
If you need to define custom rules for push distribution, you might want to include them in 'user defined distribution' under PUSH Distribution rules.
Hope that helps.
Regards,
Shweta