The AppBuilder automatically updates the size of the control whenever you use the mouse to adjust the resize handles. These resize handles actually belong to the control-frame and the ActiveX control generally conforms to the dimensions you set for the control-frame.
There are some exceptions to this. Some controls depend on a specific size. For example, if the control is represented by an icon, it expects to be sized appropriately (for example, 32 pixels square). Another example is a combo box that expects its size to be only high enough to hold its text. For controls like these, if the user tries to resize the control-frame in a way that violates its internal sizing rules, the control automatically snaps back to the size that it requires. In this case, the control-frame resizes to fit the control rather than the other way around.
For resizable controls, these adjustments update the HEIGHT-CHARS, HEIGHT-PIXELS, WIDTH-CHARS, and WIDTH-PIXELS attributes of the control-frame widget (and the corresponding control-frame COM object properties). You can also modify these attributes manually in the Property Sheet of the control-frame.