Closing one of two (or more) composition panels should make your other composition panels larger.
Currently when you have two more composition panels open (i.e. one is locked and you are making changes in a precomp and looking at the effects of that change in a different comp), the default behavior when you close one of those composition panels is to collapse any surrounding panels inward, leaving the other composition panels the same size.
This is annoying, because rarely do you want the effect control panel or your plug-in panel to expand. What you usually want is for the other composition panel to take up the space where the two were.
Thank you for reporting this issue. Are you still experiencing this issue in the latest version of After Effects ( 18.0 )?
In trying a similar panel layout to your screenshots, I am seeing the desired behavior you describe: the viewer panel ( Composition panel ) fills in the space created by closing the other viewer panel. The Project panel doesn't expand as shown in "two comps 02.png".
It's possible that there is another factor causing the unwanted behavior, possibly one of the ScriptUI panels. Does the unwanted resize happen in a workspace without those panels? There is also the possibility that the order in which the panels are opened or nested may be a factor as well.
Hoping we can get to the bottom of this, thanks for any additional information,
- John, After Effects Engineering Team