In this paper, the different contributions to the permittivity of a 1% manganese-doped BaSrTiO3 thin film are presented as a function of the applied DC field. The hyperbolic law has been used to discern the lattice, domain wall vibration, and pinning/unpinning contributions. This decomposition permits us to study the weight of the respective contribution in the total permittivity, the losses, and the tunability. By determining the figure of merit (FoM) of each contribution, the ratio between tun-ability and losses, it is possible to identify the phenomenon which should be limited or enhanced in order to optimize the material's dielectric properties. It is shown that the tunability of the domain wall contribution (approximately 80%) is very important compared to the lattice contribution (41%), the associated dissipation factor, however, is also much larger (0.2 instead of 0.014). Even if the domain wall contribution has been shown to be weak in the investigated thin film (less than 3% in permittivity and tunability), the weight of the losses is not negligible (around 18%). Hence, the domain contribution has to be limited in order to conserve a high FoM for the material. Moreover, it is shown that the AC field used for the material's characterization is important because it governs the weight of the domain wall losses and thus the FoM.