I suspect the maturity and processing of the leaves have more of an effect than the cultivar. If this effect is being observed in both coffee and tea, my guess

I suspect the maturity and processing of the leaves have more of an effect than the cultivar. If this effect is being observed in both coffee and tea, my guesses would be it's either caffeine, something with the roasting, possibly fermentation (but I'm not sure if all tea is fermented), something with fluid consumption, or something with the mental ritual of drinking mild stimulants.