Secret to flat cakes: wet cake strips (i., Bake Even Strips) and wrap around the cake pans. They act as an insulator to help the cake bake evenly (flat). You can also use strips of towel: drench, wrap around the pans, and bake.
DIY Bake Even Strips- works great to get a flat cake top! Cut 2 inch strips out of an old towel. Wet the strip with cold water. It should be wet, but not dripping. Wrap the wet cloth around the cake pan and tie or pin.