Left: sketch of the coronal X-ray source geometry, as seen by RHESSI. The lower temperature plasma is located below the higher temperature plasma. A small volume of emitting plasma dV = A dz = Ld dz varies with altitude z. Right: cartoon of the X-ray distribution versus z at energies ϵ₀₁<ϵ₀₂<ϵ₀₃ created by varying temperature T and n²A distributions with altitude z. The peak X-ray positions at a given energy, as viewed by RHESSI, are related to a T and n²A value at that position.