This is a statement of basic aerodynamic and thermodynamic principles regarding atmospheric entry, so no citation is needed.
The claim states that increasing contact surface during atmospheric reentry increases aerodynamic drag and thermal load. This follows directly from fundamental aerodynamic and thermodynamic principles (larger surface area in supersonic/hypersonic flow increases skin friction, pressure drag, and the overall convective heat flux footprint). Therefore, it is common knowledge by direct physical definition and everyday aerospace engineering observation.