With "Focus Box" I believe you mean the "Navigator" window?
Anyway, yes, of course, you can resize any window of eXposure. First, one can have them in "Movable", "Floating" or "Transparent Mode".
By default, the windows are in a certain position, when opening eXposure the first time: from there one can go to the edge of each window, and resize them up to a certain limit, given by the monitor size and the layout (see screenshot).
Or one can drag them "out" of their actual position/framing (when "Movable" is selected ---> see screenshots for how to set: one can do it either by the Menu, or then by clicking the little "screen" icon on the top right side of the window, beside the "X" and over the "i" ): this will "liberate" the window (see screenshot), which can then be re-sized at will (see screenshot), or placed on a second monitor. To bring it back to its original frame (or anywhere else), simply drag it in the place you want: the space will "Open" and the window jumps then in place (see screenshot).
There are many other possibilities, one can bring any window in another "Set" of plugins", one can move full "Sets" of plugins (e.g. also the contact sheet) from the bottom to the right or left side, etc ... It is almost un-limited.
If you wish really to make use of all the possibilities, about windows position, re-sizing or ANY other feature, it would be good to read the "on-line help": all is described there.
Another question: do the focus boxes allow for resizing? I.E.: can they be made larger? I photograph small products with fine detail and right now the focus windows are narrow vertical windows. Thanks for all your help.