Zone 2 hours - long/short vs even duration

Is anything known scientifically, or in coach’s experiences, about the difference in training adaptation and fatigue generated by Zone 2 training blocks that are equivalent in total time, but distributed evenly vs unevenly in terms of duration? For example, let’s say you have 15 hours of Zone 2 to do in a week (let’s assume this is base training, so no intervals scheduled). There are a lot of ways to divide those 15 hours, but it seems that I often see pro riders braking this up unevenly, like: 5 hrs, 2 hrs, 4 hrs, 0 hrs, 4 hrs, instead of something like: 5 days of three hours and two rest days.
Is the reason for this that you get more training benefit from the longer rides, and more recovery from the short days, vs medium, medium, etc.? I’ve tried both, and anecdotally the latter seems to generate more fatigue, but I have no idea about any differences in training benefits between the two approaches.