No, because of variable illumination current, Rs of cells and switcher circuitry, the switcher duty cycle must adjust to account for these changes. The 0.76 has nothing to do with switcher duty cycle.
The switcher regulates based on input voltage sense instead of conventional switcher output voltage sense.
The "0.76" factor between Voc and Vmp depends on series resistance of cells and their illumination current output. I would say 0.76 is too low. At 25 degs C Vmp is about 0.52v where Voc is about 0.66 vdc. Mono-crystaline cells have lower Rs and the factor would be more like 0.81. Poly-crystaline would be more like 0.79.
You want to avoid going too high in voltage where inherent cell diode conduction goes up exponentially so the 0.76 is likely to ensure you always stay down on the more constant current region. You will loose some available power by doing this over a more efficient MPPT algorythm.
If charging a battery the simplest and most effective MPPT algorythm is to just maximize the battery charging current.