Focal Length vs Field of View
I just tried the same thing with my FZ40 in both iA and P. In P the zoom goes to full optical, 24x. In iA the zoom goes to full optical plus the extended zoom, and it shows the zoom being 32x. To achieve the 32x with only 24x optical zoom, the camera crops off some of the picture, and increases the size of the center bit. Both of these shots were at 108 mm.
I got noticeably better detail using the extended zoom, so if you don't feel like PP after the fact, then shooting in iA looks like it would work the best, at least for long range shots.