By depth I meant thickness. But thickness sideways doesn't help nearly as much as thickness in the vertical direction. A beam with a bending load like here can

By depth I meant thickness. But thickness sideways doesn't help nearly as much as thickness in the vertical direction. A beam with a bending load like here can crack from the bending at the middle for example. The fasteners at the ends are not necessarily the limit. It's different for pure compression or tension, there the fastener area sees higher load.