The relative impact of edge localized modes (ELM) size and plasma shape on the antenna coupling in ASDEX Upgrade discharges is studied. A strong dependence of relative change in the ion cyclotron range of frequencies antenna coupling during ELMs on the ELM size is observed. The changes in the coupling also show some dependence on the plasma triangularity; the latter generally influences the ELM size. At high plasma density and small antenna–plasma distance, however, there is a strong residual correlation of the antenna coupling on the plasma triangularity which appears not to be connected with the ELM size. A possible explanation of this correlation is given in terms of the connection lengths of the magnetic field lines at the antenna. This hypothesis is substantiated by the investigation of L-mode discharges, which are better diagnosed than the ELM phases of the H-mode ones.