It's kind of a trial-and-error thing, Mo, so I can't really post an explanation (or maybe it would be more honest to say that I don't really know the answer...) ALLCAPS titles take up more space, so fewer letters are allowed. If your title includes a preponderance of lowercase letter "i," you can fit in lots of letters. If it's mostly uppercase "M," you're not so lucky.

If the title doesn't turn out the way you want it, contact me, or one of your friendly local JoeClones.

Oh, and please note that we don't usually allow ALLCAPS in thread titles, although there may be exceptions at times. We also expect titles to be reasonably specific, and to reflect what's in the thread.
-Joe Offer-