When I was setting up printing on my laptop, I ran into some issue where the cups test page would come out flawlessly, but trying to print via browser, or via command line (lp, lpr, a2ps, vim's :hardcopy, etc) would result in the page being shifted down and the last ~inch being cut off.

The solutions other people posted online didn't quite fix my issue, so give this a shot if you find yourself the same scenario.

Make sure you have both of these packages installed from the Arch User Repository:

brother-9320cw-cups-bin 1.1.2-1
        brother-9320cw-lpr-bin 1.1.2-1

Command Line Printing

From the a2ps manual online or via man a2ps or info a2ps:

a2ps reads several files before the command line options. In order, they are:
        1. the system configuration file (typically /usr/local/etc/a2ps.cfg) unless you have defined the environment variable ‘A2PS_CONFIG’, in which case a2ps reads the file it points to;
        2. the user’s home configuration file ($HOME/.a2ps/a2psrc)
        3. the local file (./.a2psrc)

I know that I'm only ever going to be printing on letter sized paper, so I added the following to my configuration file ~/.a2ps/a2psrc:

Options: --medium=Letter
        # Letter for Brother Printer
        #       name        w       h       11x     lly     urx     ury
        Medium: Letter      612     792     12      72      576     792

Explained in the manual:

where wxh are the dimension of the sheet, and the four other stand for lower left x and y, upper right x and y
        (...)
        If for instance you want to use Letter as medium, then use:
        Options: --medium=Letter
        It is exactly the same as always giving a2ps the option ‘--medium=Letter’ at run time.

This is good enough for vim's :hardcopy, passing a .pdf attachment out of neomutt, and that sort of thing, if your needs are more complicated then this will work as a baseline configuration.

Printing via Browser/System Dialog

Go to the cups webGUI by connecting to http://localhost:631 in your browser, go to printer and select yours, then in the second dropdown menu click on set default options and use your linux login when challenged

Cups > Printer > Set Default Options

Media Size: Custom 
        Width: 612 
        Height: 792 
        Units: Points

EDIT: UPDATE PT2