Could it be said that tournaments are played from combo tees?
For normal play, each set of tees is put in about the same place every day (somewhere on the same box). I have played very few tournaments that have the tees all at the back box for all the rounds. They are usually moved each day, and sometimes quite a bit. I do realized that a combo set does dictate which box to play on each hole, and therefore, would in essence have the same issue as the regular tees markers.
I recently played a tournament at a short municipal course (6200 yard par 70). I was surprised at how they set it up, but it was extremely fun. Almost no hole played the same box for all three days. They used the most forward box on a few holes on a couple of days. A 360 yard par 4 was played at 275, a 515 yard par 5 was played at 470, and another 510 yard par 5 was played at 450. Other holes were moved from box to box, but not as dramatically. It was great fun, and scores were not super low. Many of the new tees brought trouble into play that you really didn't even know was there from the back tees.