We analyzed molecular ordering in the nematic phase of cyclic LC oligomers with mesogenic groups attached to a central siloxane ring. We focus on relationships between the local spatial arrangement of these molecules and low-angle X-ray scattering phenomena as revealed by computer molecular modeling. Computer simulation shows that the presence of strong low-angle X-ray reflections in the nematic phase is caused by local association of the molecules. The cyclic molecules form double-row associations with up to six molecules packed in a single string. The presence of the siloxane central rings with a high local concentration of Si-O atomic groups with strong scattering power is critical for the appearance of these low-angle X-ray reflections with significant intensity. Cycling of siloxane groups into short rings hinders rotation and restricts mobility of these fragments, resulting in a high localization of strong scattering groups. Computer simulation of X-ray properties of partially ordered systems within the "lattice approximation" works well for crystal lattices and highly ordered mesophases like smectics. However, this approach underestimates local distortions of positional ordering and does not adequately describe short-range molecular ordering in the nematic phase. Application of straightforward calculations of the form-factor of molecular clusters reproduces major features of these unusual X-ray scattering patterns but falls short in describing fine details such as diffuse background scattering, peak profiles, and exact d-spacings.