reading over everything again, i'm realizing that there is a communication problem between aesir and myself and possibly others. First off, yes, the utilt DOES work at 32%, but I disagree that fox easily DIs out of it. I believe that fox can still be regrabbed with a dash grab even with DI from the utilt. I'll test this some more in the future. However, I've found that I have been able to regrab with or without the utilt at that percent due to the fact that marth's grab outranges shine and the fact that you can often grab them before they are able to shine. The choice of whether to utilt or just regrab is pretty intuitive, and basically depends on fox's DI. 29% however, is too low of a percent to do utilt if you're expecting to get the right knockback for a regrab. I personally find 29% to be a much more difficult percent than 32 to figure out since that's the point where fox can probably most easily shine and jump, but without being hit by utilt in such a way that pops him up for a regrab. This is where the pivot grab comes in since it can put you in range for a safer grab at that percent. I tested this playing against a fox yesterday, so I know for a fact that this definitely works.
Now, the miscommunication lies in the earlier post where aesir says that Fox can escape by jumping out a shining. Perhaps you meant only if the marth messes up, but to me i got the impression that it meant that marth's chaingrab/utilts/aerials/etc ends at that point. Either way, I'm going to say that marth still has the ability to definitely combo fox with a combination or grabs (and utilts when necessary) to well beyond 32.
phew, done with that wall of text. man, i need something to do at work. i've just been on smashboards too much these last two days >_<