I don’t understand why the Sources For (Citation List Pane) window would re-attach itself to the Property Box.
Open the Tools > Preferences > Property Box tab and check that both ‘Preferred Position for Citation List Pane’ options are set to ‘Open in New Window’.
Assuming you usually only have two or three Source Citations then make the Sources For (Citation List Pane) window shorter.
i.e. Drag its bottom edge upwards so it does not overlap the Citation window.
There is not much you can do to the Citation window if you want all those Citation-specific fields displayed.
Before you close FH, make sure both those windows are open, positioned & sized the way you want them.
Then when FH is reopened, and those windows are opened, they should retain their position & size.
BTW: You don’t seem to have Voted for Wish List Ref 534 Preserve all Workspace and Window Characteristics