Infusion systems, infusion devices, and related operating methods are provided. A method of operating an infusion device involves obtaining an input qualitative event attribute, such as a meal size, obtaining a quantitative event attribute associated with the qualitative event attribute that is representative of a subset of historical events for a patient associated with the qualitative event attribute, such as a representative carbohydrate amount for the qualitative meal size, and thereafter determine a dosage of fluid based at least in part on the quantitative event attribute and operate the infusion device to deliver the dosage of the fluid to the patient.