Round tomatoes have a tendency to dump over as the cheese soufflés rise. There are several ways to address this… A) Press the tomato bottoms flat before baking. B) Make a double batch and stuff more tomatoes in the pan. C) Find a pan that the tomatoes fit tightly into, possibly a 9 X 9-inch pan. D) You can even make foil rings to set each tomato in to hold them straight. However, I find, if you flatten the bottom well, this usually fixes the problem.