You can try adjusting the minimum size in the project settings (Client // User Interface). It should allow the windows to shrink down to it. There is also a minimum size setting for each window, but it defaults to 0 x 0. May still be good to look for a sanity check.
From a personal design standpoint, I set minimum size to 10 x 10 pixels smaller than the lowest resolution I want to support. Then I design the windows to fit that minimum size.