Yes, Crowbar, thank you for pointing out that some strength comes from the web itself, especially when you consider the h cubed terms contribution, just trying to simplify things, since the original question was keeping the vertical distance constant, and just increasing the width.  With structural steel, with thick webs, there is a significant contibution due to the web, but in many other materials or combinations, where weight savings is a concern, the webs are made as thin or light as possible letting the flanges take most of the load.  I'm picturing an engineered floor truss with 1.5 inch thick flanges and 3/8 thick discontinuous web.