When a statute renders a defendant presumptively ineligible for probation, how does the court determine whether the presumption against probation is overcome?

When a statute renders a defendant presumptively ineligible for probation, a court determines whether the presumption against probation is overcome pursuant to the criteria set forth in rule 4.413. The existence of a factor set out in rule 4.413 may indicate the existence of an unusual case, but such a finding is permissive, not mandatory; i.e., " '[t]he trial court may but is not required to find the case unusual if the relevant criterion is met under each of the subdivisions.' " (People v. Stuart (2007) 156 Cal.App.4th 165, 178.)