You're right, the MCD windows and its component sections are all fixed and can't be adjusted independently like the in the main PD window.

You can make the MCD tool full screen, and while that makes the preview window much larger and shows a much longer stretch of the timeline, it doesn't change the actual sizes of the media windows, the controls or the height of the timeline tracks.

You can let CL know that you'd like to see the ability to adjust the sizes of the MCD window components by using Rate Us & Provide Suggestions under PD's File menu.