The differences at the low end of the chart are the startup costs, which get amortised out at the high end. You could only return bools in the flags for static

The differences at the low end of the chart are the startup costs, which get amortised out at the high end. You could only return bools in the flags for static functions that don't have their address taken, because this would break the established API. It'd also generally only be useful if the function result is immediately used in a test.