In the montage you cannot change the horizontal size of the lowest track by dragging

Is there a reason for this? Thanks in advance.

I guess you mean “vertical size” because there is no concept of “horizontal size” for a given track.
You can. Just drag this separator.

OK I guess it is a matter of semantics…To me the lines are horizontal so that is the description I chose.

Anyway…

Try and move the lowest track size by dragging from the bottom of the screen. It works on all the other tracks but not the lowest track. Is there a reason for this behaviour? Thanks!

So you can make it “bigger” but not “smaller”???

Also, you can work with shortcuts.