Actually, many trapshooters are hideously overchoked for singles,Mark. The revolution in ammunition that followed plastic cases, wads, hard shot and better powders and primers have basically kicked performance up a notch, as that loudmouth on the Food Channel would say. Some local legends that are fast use a Light Modified for singles and bust them all regularly.
However, there may be a good reason to go to a very tight choke. I did when I started shooting trap, Jan 01. The ultra tight pattern not only teaches me to hold tighter, but it's easier to read my breaks and see where the pattern is going.
Bill Gillete, the Shotgun Sage at Big Ridge Gunsmithing, says that the bast all round choke for trap is a constriction of .025". That's considered Improved Modified most places, or Light Full, depending on whose chart you're using.
Also, regardless of the markings on the choke or bbl, it takes patterning to determine just what choke and load works best for you at the distance you're breaking your birds.
What we want is the largest pattern we can get that has lots of pellets in the fringe but no flyers outside the pattern, and no holes. Those who make more of a science out of this tell us that one pellet of 8 1/2 size or larget in each two square inches is enough to bust clays, but I'd rather see something like 2 pellets. The More is Better Principle.
And while people keep talking about a 30" pattern, for the proper density it's more likely to be a good 24-28" pattern.
While I'm no local legend, if I were using a tube choked shotgun, I'd use Light Modified or Modified back to the 20 yard line, and go to an IM after that, depending on load,etc.
HTH....