> Given a word like "there's" or "that's", does the letter before the
> apostrophe count as a "last" letter?  In other words, could "that's"
> become "ttha's"?
>
> In the example above, there's no case where that letter gets
> scrambled.  It's possible that that's coincidence, but it doesn't look
> like it.

Do it whichever way you like it...

I don't know what the study said about contractions, if anything.
Personally, I think I would consider the parts before and after as
separate words, which would be slightly less scrambled, but my
intuition (which could be wrong) says that counting it as one whole
word might throw off legibility more than expected.