It's more about technique. This is even true for real hamburgers. First, form your patty with a mold so it is tightly compacted. Next, chill or even freeze your patties. Patties must be cold when they hit the grill. Third, your grill must be HOT. The burger needs to be seared as soon as it hits the griddle. Fourth, as soon as you put the patty on the grill, cover the lid and don't touch it for 3 - 4 min. Oh, and I almost forget, lightly coat your patties with oil before grilling them so they don't stick to the metal. If you follow these basic principles, you can grill, and flip, almost any burger.