  We demonstrate that a multi-peak FMR spectrum, with lines corresponding to
resonance in different ferromagnetic regions of a heterogeneous thin-film
sample, can collapse to a single-peak spectrum if there exists a particular
field configuration, or the configuration of the external magnetic field with
respect to the film surface, in which $dH_{\text{res}}/dM_{\text{eff}}=0$
within the region magnetically dominating in the sample.
