The calculation is actually easier than I’ve broken down, though speaking in terms of hours and people is less abstract perhaps.

With the figures you’ve been using the time ‘lost’ is 3.2% of total working time, so the cost is 3.2% of salary… US$1920.- in this case.

20% of 16% of total = 3.2%

Really surprised though that no-one spotted this beforehand though.