Excellent work. I did a complete spreadsheet analysis on this and numerous other pathogens several years ago. This is one reason that explains why the 2500 Hz range is so important.
It should be noted, that most 555 based units are NOT exactly 50% duty cycle but actually range from 49.5:50.5 to 45:55 due to circuit design.
MPU based units can easily provide an "almost perfect" 50 percent duty cycle.