Is the standard deduction included when using the Fixed Rate income tax mode?
The US standard deduction is only included in US Tax Estimation mode, and is not considered if you are using a fixed effective tax rate instead.
One reason for this is to support a broader set of use cases than just US-specific ones; e.g., if you were modeling an international scenario using a fixed effective tax rate, you probably wouldn’t want the US standard deduction baked into that.