LPE grown SiGe nanoscale islands on (001)Si form extended chains which are aligned along the <100> directions. The positional ordering within the island chains was studied by x-ray diffuse scattering. The results can be interpreted by a short-range order model. The corresponding correlation function exhibits an asymmetric peak profile. The asymmetry leads to non-equidistantly spaced satellite peaks which disperse outwards slightly with increasing lateral momentum transfer. The observed asymmetric island-island correlation is caused by the successive growth of the islands within a chain, while the new island position is influenced by depletion of the wetting layer around the island.