I have to say that although I now smoke tri-tips mostly, I have cooked directly and have the opinion that there are a lot of different ways to cook Santa Maria style. The guys I learned from flipped maybe 5 to 6 times total. Is that a lot of flipping, I don't think so. On the other hand, I see guys with trailer mounted grill that are on the small side and they have to flip and move the meat around to get things done right. My take on it, is that if you have the right rig and the time, you can do a good tri-tip with minimal turns. I see no scientific reason to believe that flipping would make a roast cook more evenly.
Whip It Off, Chambers!
"perhaps...but then again...maybe not..."