ты --help или man читал?

--geometry=geometry

Sets the geometry of the last-specified window to geometry.
You can use this to set the columns and rows with the format 
COLUMNSxROWS, but also to set a position +XOFF+YOFF or both 
COLUMNSxROWS+XOFF+YOFF. The offsets can also be negative to 
define a right or bottom offset. 

Спасибо, читал. В итоге про геометрию вычитал в мане X 7. Все получилось

man xfce4-terminal

--geometry=геометрия

Задать геометрию последнего указанного окна.

man X 7

GEOMETRY SPECIFICATIONS

One of the advantages of using window systems instead of hardwired terminals is that applications don't have to be restricted to a particular size or location on the screen. Although the layout of windows on a display is controlled by the window manager that the user is running (described below), most X programs accept a command line argument of the form -geometry WIDTHxHEIGHT+XOFF+YOFF (where WIDTH, HEIGHT, XOFF, and YOFF are numbers) for specifying a pre‐ ferred size and location for this application's main window.