I hate the thick crust formed on my cakes!!! 

Can anyone advise me on which rack should I place my cake at? There’s only 3 racks in my oven. I believe the thick crust is formed because it’s placed too close to the “fire”.

For cakes, I usually place them on the lowest rack so the crust is at the bottom. Is it ok if I bake with both upper and lower heat for half of the baking time, then change to upper heat for the rest of the time to prevent the (sometimes burnt) crust?