I set mine up with 11" and it sounds very similar with a step up. I ran the heat tape across the bottom and up the step in the back. If you are planning on using water bottles to hold a steady temp then you need some of the tape on the bottom as well.

Here is a picture and for some reason it looks like there are bulges in the heat tape but there are not. It sits flat and the incubator reaches temperature in 30-40 minutes and holds steady.