If it's being cooked over a hot fire on a Santa Maria style grill, then flipping frequently probably makes sense, esp when there are a lot of tri-tips and several heat zones going on. Since I don't have a Santa Maria grill, I just cook mine on the kettle indirect via reverse sear using some red oak.
For various reasons, I also try to avoid handling/moving my meat as much as possible during the cook process, so I'm usually looking at 4 or so total turns for the entire cook, and that includes two for the searing part at the end.
For me, getting the best possible tri-tip boils down to these factors:
1. The actual quality of the tri-tip. I look for USDA choice or higher, with lots of marbling and about 1/4 inch fat cap on the underside. This for me has been the greatest variable, and on occasion even pieces of meat I THOUGHT looked great didn't turn out as well as expected. But going with higher quality cuts helps a lot.
2. The seasoning - I've had great results with simple Santa Maria style rubs to more complex rubs, but don't feel the need to marinate the meat.
3. How the meat is cooked - again, I've had better results with reverse searing than the usual method, in addition to using some oak for flavor. Oak just seems to be the perfect compliment to Tri-Tip, but I've also had good results with Pecan as well.
4 - The obvious: letting the meat sit for at least 10 mins before slicing, and then slicing against the grain.
Honestly, compared to these 4 factors, flipping frequently isn't going to make a noticeable difference.
Just my $.01...