The timing can also play into it (not sure if by 'plan' you mean down to the hour as well). https://i.imgur.com/1IyKjSg.jpg
As I get older, my tolerance has lowered. I used to be able to handle a Starbucks 'tall' cup, but now I can only drink two espressos at most, if spaced out by two hours or so. If I go over my limit, it's 7-9 hours of lying still in a dark room with a migraine-like headache.
For more on cortisol and caffeine: https://www.forbes.com/sites/anthonykosner/2014/01/05/why-th...
Chronopharmocology and caffeine: http://neurosciencedc.blogspot.com/2013/10/the-best-time-for...