Interlayer exchange coupling was investigated in highly Co-enriched (75.6 at. %), i.e., in Co antisite defective Heusler alloy Co-Mn-Si–based epitaxial trilayer structures for a wide range of spacer Cr thicknesses (tCr). The exchange coupling parameters J1 (bilinear coupling) and J2 (90° coupling) were estimated from the comparison of experimental and numerical simulations of M-H loops. The comparable contributions of both the bilinear and 90° couplings were observed in a spacer thickness range, tCr ∼ 0.3 to 4.2 nm. The relative angle of magnetization at remanence between the bottom and top Co-Mn-Si layers was found to vary from 67° to a maximum of 152° as a result of competition between bilinear and 90° couplings. In contrast to the observation of strong 90° coupling without any detectable bilinear type 180° coupling in almost stoichiometric and chemically B2-ordered Co2MnSi-based trilayer structures in a previous study, the results in this study clearly indicated the importance of the effect of chemical ordering on dominating 90° coupling in Heusler alloy–based structures.