Right now ACP template editor in XenForo doesn't fully utilize all available window height, it only has a small window of 325 pixels height and 900 pixels width. You can extend it of course manually, but repeating this operation over and over again personally drives me crazy. Of course you can write your own script, but it will be overwritten after the next update. I spend a lot of time in XenForo template editor and wish it had more space available. BTW the same thing applies to window width.