Staring at the cake, it looked small, so after I put my son to bed I decided to make a second cake. I have about 15 coworkers at any given meeting, and the cake supposedly serves 8-10. 8-10 munchkins, or non-hungry people eating a slice to be polite, maybe.
So I scrapped the previous recipe and went back to one I've used before, the Too Much Chocolate Cake, from AllRecipes. This is another cake mix cake, but I didn't have any coffee to use and it called for fewer eggs, so I was hopeful of a lighter, less fudgy result that wouldn't fall.
I also did a bit more reading on cake release, and found that some people added an extra 1/2 cup of oil to their mixture. I drizzled in about 1/3 cup and mixed it up. This mixture coated the pan much better.
Upon baking for about 45 minutes (no opening the oven prematurely this time), Cake #2 emerged from the oven puffy and delicious-smelling, and turned out of the pan with ease.