There is a setting in the Global Options that can control this to some extent. This is "limit annotation size for new icons" under the "Flowchart" tab.
However, this only works for newly created flowchart icons.
This setting controls a hidden property of each icon called "textarea". You could change this manually for any icons by directly editing the project fcfx file in a text editor. Of course, if you do this then be careful - make a backup of the file and change only the specific entry.
The attached project shows what I mean. It has 3 icons. The first was added when the annotation size limit is off and the second was added when the limit is on. The third is one where I have manually added the "textarea" for the icon within the project file.
