The default sponsor share of a trader's mint fee (20%), and the rate the chain reads while the
admin hasn't set one.
Deprecated
From delayed execution (DBU-885) the rate is admin-set: read it with
protocol_config::fee_incentive_subsidy_rate (read.queue(...).protocol.feeIncentiveSubsidyRate)
and pass it as feeIncentiveSubsidyRate. A hardcoded 20% underquotes every mint once the rate
moves.
The default sponsor share of a trader's mint fee (20%), and the rate the chain reads while the admin hasn't set one.