Sizing the storage tank for a solar water heater system

Hello,

I am sizing a solar water system and I am trying to find the perfect match between the collectors area and the storage volume. For large designs professionals seem to recommend that storage volume should always be greater than the site's average daily use. In regions with considerable sunlight, they also advise a 2 gallons increase in storage every square foot of net aperture area, in order to prevent the system for overheating during peak hours.

Through SAM I find that I can decrease my storage volume to less than half of the daily consumption and still have a solar fraction of 80%, with a reasonable amount of collectors. How is the system able to provide hot water with such a small tank and with a good solar fraction ? What about the possibility of overheating ?

Thank you for your help.