I agree in some photos the aircraft do seem to have the thrust line pointed in a downward direction, optical illusion or not I don't know.
It may be that the centre of gravity is above the thrust line, therefore an increase in power would tend to make the aircraft pitch up. The thrust line is then pointed down as a means of controlling the pitch up.
Just a blind guess, look at a photo of a T-28 to see a very prominent downward pointing thrust line.
As john_tullamarine says elsewhere, "Design is a compromise to make a lot of conflicting task and systems needs all fit and work reasonably well together.
Unless you have a list of all the relevant considerations which went into the design configuration definition exercise, there is no way you can infer much at all with any real confidence".