If you are viewing tasks, and not projects with their associated tasks, you want to use context mode, group by completed (or ungrouped), sort by completed, and I think you'll get what you want. The grouping choice doesn't sort the contents of a given group, and if you are in project mode, everything is done on a project basis.
I have a "Completed today" perspective which is context mode, grouped by completed, sort by project, completed actions, all durations and all flag states. The "completed today" group is open, and the rest are closed. Actual completion of complete projects is relatively rare for me because so many of them are ongoing with no fixed endpoint, so sorting by project rather than completion date gets me a better view of where my effort has gone as I'm generally not looking back trying to figure out what I spent my time on a week ago Thursday. If I had to characterize my time use on a daily basis over the last 2 weeks for a timesheet, I would probably sort by completed instead.