Though many traditional synthesis techniques have been successful in reproducing the sounds of musical instruments, several of these techniques require setting parameters, a task that can be difficult and time-consuming especially when there is not intuitive correspondence between a parameter value and the change in the produced sound. Finding and setting a synthesis algorithm's parameter space is, therefore, a task more naturally suited to an automatic optimization scheme. Genetic algorithms (GA) have been used rather extensively for this purpose, and in particular for calibrating FM synthesis to recorded (musical) sound. In this work, we use GA to further explore its modified counterpart, Modified FM (ModFM), which has not been used as widely, and its ability to produce musical sound not as fully explored. We refine a genetic algorithm that determines optimized parameters for the reconstruction of harmonic instrument tones using ModFM. In an evaluation, we show that the GA system automatically generates harmonic musical instrument sounds closely matching the target recordings, a match comparable to the application of GA to classic FM synthesis.