How many cups of cake batter do you all normally put in a quarter sheet cake pan (2" tall)? I keep getting tons of excess cake that all seems to bubble in the middle. As of now I'm just using the entire box of cake mix...Any suggestions?

Do you have any tips for how much batter I should be filling smaller pans/round pans?

One thing that will help with your rectangle cakes is to put a flower nail upside down in the middle of the pan before you put the batter in, and then bake at 325 instead of 350. That will help it bake flatter. I think the reason that the middle ends up doming is because the middle cooks last and has nowhere to go but up, but when you put the flower nail in it acts as a heating core and the middle cooks faster so it doesn't stick up as far. I usually overfill the pan a bit...not so much that it overflows (at least hopefully not) but more than it says in the Wilton chart because I want nice, tall layers.

I also tie old towels around all my pans to get them to bake evenly. Just cut a scrap towel about 2" wide and either tie or safety pin it to the pan. Be sure to wet and ring out the towel first. Works just like a bake-even strip.