This is so very simple. if you are not a lousy cook then it’s got to be in the air. That’s right air flow is a big part of cooking evenly which is why convection cooking has become so popular. There is one simple thing that you can do. check the oven with a level and see if it is level where it sits whether it’s a wall oven or a free standing range it must be level inside to evenly cook and do not put the foil on the bottom of the oven or even on the rack. This may make it easier to clean, well unless it sticks to bottom and peals the porcelain right off when you remove it. It is an air impedance and remember that air flow is essential for even cooking and if you do two tier cooking then that pamphlet that is called owners manual or use and care guide can teach you how to do this correctly. I may sound like I am telling you how to cook, but if you want the best results then utilize what the manufacturer paid the engineers to do. Test after test based on what you asked for in the first place. Almost every manufacturer has an online manual if you can’t find yours. This could make the oven you don’t like one that you brag about.