Silicon adatoms can occupy either the H3 or T4 site, corresponding to the hollow or on-top site of the hexagonal unit cell of the 6H-SiC(0001)-root3xroot3R30degrees superstructure. Distinguishing these two possibilities is impossible with the one-beam calculation method in surface electron diffraction. We provide the experimental evidence to differentiate between these two possibilities using a dynamic, multiple rocking beam approach and demonstrate the sensitivity of this approach to the lateral displacement of atoms on the surface. Our study shows that the rocking curve based on the T4 model provides a more convincing fit to the experiment compared with the H3 model, with a metric distance as low as 7%. We also identify A-type termination to be the most likely bulk-truncated substrate face among the three possible truncated faces for the 6H-SiC polytype. Coverage dependence of the silicon adatoms on the profile of the rocking curve is also investigated. (C) 2003 American Institute of Physics.