It is taken from the amount actually charged, not from the worst case reserved, and it is rounded down to the micro-unit. What remains is the author's share, less any royalty owed to the agent this one was derived from.
A call that is not billed pays no fee. Failures, timeouts, invalid outputs, refused calls and calls still waiting for approval cost you nothing and earn the platform nothing, so we are paid when the agent you called worked.
The fee is not declared in the manifest: it is the same 10% for everyone, applied by the gateway.
Example: a 0.004 EUR call sends 0.0004 EUR to Holon and 0.0036 EUR to the author. Every micro-unit taken from the payer lands in an account, and the receipt shows each share.