Here, I will show a few example screenshots from the original subtitled MKV file of Toki wo Kakeru Shoujo from roxfan (Played and captured screenshots using Media Player Classic) and the output from our 46" Samsung DLP Widescreen TV using my repositioned version of the roxfan script (Using the highly technical process of playing the movie on the TV and capturing screenshots using a digital camera). The widescreen TV was using an older version of my original adjustments (The "TV" subtitles were actually placed too low; I had fixed that in the attached file, but didn't get pics of it).
Here's a good example of how much left and right screen space is lost from the overscan:
As you can see, the subtitle was forced to two lines as a result of a lost of only 6.5% of screen space on each horizontal side (Though this gives 13% total lost area in the horizontal space). Truthfully, this one came extremely close on the original output to the screen (I think the "Y" was halfway cut off), but I found it much more comfortable to read when it was forced to two lines.
The following is an even better example:
As you should be able to see, the left florescent light on the ceiling is completely off-screen, and so is the very right column of window panes and Kousuke's shoulder. Chiaki's chair also almost disappears. The original subtitle position would have almost worked except letters that extend below the basline ("p", "q", "j", or "g", for some examples) would have been cut off at the bottom of the screen. Though, comparing these two screens, it seems that there's not much cut off at the top of the screen (but still some).
Here's an example of a song being translated (with the original Japanese words being shown):
In this case, the original subtitle positions would have had "wake" and "I was" nearly completely cut off, and the first line would have had the very tops of the letters on the edge of the screen. As it is, even the adjusted lyrics ran right on the left side of the screen. A bit more padding on the left and right sides might have been a good idea.
From what I understand, most professional broadcasters and video producers assume a certain amount of overscan (It seems the numbers used are available on this Wikipedia page.). It would be nice if more fansub groups would also follow the same numbers, but if they continue to release MKVs with soft-subs, it will always be possible to adjust the margins of the subtitles for ourselves.