Reading these numbers
Start with the hours. Most people have two or three hours in the day when their sessions actually finish, and those hours are usually earlier or later than they assume. Once you can see yours, defend them: no meetings, no errands, nothing that can be moved to a weaker part of the day.
Four to five focus sessions is a strong day, not a weak one. Ericsson's studies of expert performers found that even violinists at the top of their conservatory rarely sustained more than about four hours of deliberate practice a day, spread across the morning and afternoon with rest between. If your daily totals sit near that, the constraint is real rather than a discipline problem.
The estimated versus actual ratio is the most useful line on this page. Treat it as a personal multiplier. If your completed tasks came in at 150 percent of estimate, a task that feels like four sessions is a six-session task, and planning it as six is what stops the week from sliding.
Watch the 14-day chart for shape rather than height. Long flat stretches broken by one tall day usually mean the work is being pushed to deadlines, which costs more than a steady three sessions a day would.