Man hours per hour flown like all statistics can be misleading.
Heavy maintenance hours for instance would be included in the figures but are not relevent if a replacement aircraft is put in place on an operation.
Does this figure include washing, towing, starts, turn rounds. e.t.c.
If you have a duty line crew these hours are "covered".
As an example the 139 goes in for heavy maintenance every 1200 hours off line for about 2 weeks, no effect on the line maintenace man hours for the operational aircraft.
If the figure of 400 hours a year is about right then that is every 3 years.
As the aircraft mature the 1200 hour will probably escalate giving a greater period between checks but with more down time as the aircraft get older.
Is there a spare aircraft available, how the maintenace program is organised, and aircraft reliability are the issues that are more important than a flying hour versus man hour figure.
The size of the windows made available for scheduled maintenance have an effect, smaller the window the better organised you have to be and more people might be needed.
Again you can only get so many people in one hole!!!!!