A bit late on my response, but we have found the thrust angle you set the engine at does determine the elevator trim. At the "stunt" setting, you do not need as much up elevator when compared to the beginner thrust position. PT-19s seem to fly at a pretty high angle of attack due to the decalage/incidence relationship between the wing and stab, so it's normal to see what your picture shows. Most Cox plastic planes were similar in that they were best at doing gentle climbs and dives, nothing really sudden or radical, and you needed to initiate a climb well in advance to avoid a "ground swell". The all balsa slab wing trainers by Guillows, Goldberg, and Sterling were far better flyers and responded much better, in fact it was not until I had built and flown a 1/2A balsa plane that I was able to sucessfully fly a plastic Cox plane. With a teacher however, most kids can gain control of a PT-19 with a few minutes of flight training on a calm day.

All of the PT-19s with a seperate plastic fuel tanks have a a further aft CG because the early metal tank Baby Bee was heavier. Have not really noticed much difference in the way they fly due to that, because the biggest difference is with the lighter lines, and the wing tip weight adding more control feel at the handle.