There actually are comprehensive studies of reader behavior relative to type style, point size, leading, line length and more. The best-known of them is now some 60 years old. I'd love to see one as extensive today when at the last generation or two has grown up reading from a screen and not paper.
Yeah, any 60 year old study is going to be bad on its face, as that was when things were still done with actual typesetting and the styles and point sizes were determined by equipment capacity.
Even a decade ago, the difference between offset printing and print-on-demand meant that certain formats were determined by HOW the book was printed, not any special readability per se. (disclosure: I work in contract packaging and our company uses offset and litho presses as well as POD machines.) Reader expectations have traditionally be set by machine limitations.
For example, the "mass market paperback" size. People will SWEAR there is some magical, wonderful reason for this that involves it being the perfect size to fit in a bag or carry over trade paperback size. It is all nonsense and revisionist thinking to justify the continued use of a size that no longer makes financial sense. The mass market size is a product of cheap production value. Go look at old mass market paperbacks (or even those produced by big publishers today). The paper quality and cover stock is cheaper. The size was created to get the maximum number of books off the press using the cheapest paper possible to control costs. That was it. Had nothing to do with magical perfect size for a beach read. It was a production decision based on cost controls. Trade paperback size cost more because the machine produced fewer pages per sheet.
In POD, there is no difference in cost because the production process is the same regardless of the trim size. So using a smaller size only INCREASES your production cost because it pushes up your page count, and you pay by the page for POD production.
My point is, what you may be seeing from those old studies isn't some "reader preference," but the result of reader programming based on what the publishers were already doing do to the limitations of the equipment at the time.
There are readability issues between screen and print that a formatter should take into consideration. But it is important to differentiate "stuff we've always done this way because the machines only worked that way" and "what is the best option TODAY for what I am trying to do?"