Graphic adjustment when resizing a 3D Viewer

Hello everybody,
as the window hosting my OCC application can be resized, I've noticed that the zoom factor is adjusted in some way (sometimes) when the user changes the window sizes. More in detail, I've seen that when the X size is modified, the zoom level tends to stay the same as long as the scene length is (more or less) equal to the scene width, without caring if the visibility of the scene changes (some objects to the left or to the right could be hidden by the narrowed borders of the viewer). When the window becomes narrower, then a zoom out operation is automatically performed (it appears) in order to keep the visibility qualitatively similar along the Y axis. If the width of the viewer is changed instead, a zoom in or out operation is immediately performed as if the Y dimension is somehow to be kept into account more than the X one. At first I though it was a problem in my application but I saw that also a sample application coming with the C# wrapper (which I'm using) has the same behaviour (see attached pictures, where the zoom in or out is done only in certain circumstances)
I was expecting that a zoom in or out operation is performed every time there is a resize of the viewer. Is it possible to get such a behaviour? Or, other than that, is it possible to disable any zoom in or out operation when resizing the viewer?
Many thanks in advance for your help.

Gianluca