Can you add to the options that if there are no tabs currently open that whatever is opened will fill the screen by default.
Not opening to only the left side (half the screen). Always fill the available space (The "1 Tile" layout option).
In the tab header options you could add a checbox somewhere that the particular book or tool would disregard the default.
If I want only that thing to always open on one half I could make it an exception to the rule.