Here are the category items and their totals for an example.
The grader report shows a total of 227.2.
The user report shows a total of 260.75, which is calculated from 2.8972/7 * (694 - 64) = 260.75
This is clearly faulty logic because it sums and averages the percentages for each category as if they each have the same weight.
The path through the code is roughly as follows:
blank_hidden_total (in grade/report/lib.php) calls get_hiding_affected (in lib/grade/grade_grade.php).
get_hiding_affected calls standardise_score (which essentially computes percentages in this case).
get_hiding_affected calls aggregate_values (which sums the percentages)
get_hiding_affected calls standardise_score to rescale relative to max grade.