A large arsenal of space-based and ground-based instruments is dedicated to the observation of radio emissions, whether they originate within our solar system or not. Radio photons interact with anisotropic density fluctuations in the heliosphere, which can alter their trajectory and influence properties deduced from observations. This is particularly evident in solar radio observations, where anisotropic scattering leads to highly-directional radio emissions. Consequently, observers at varying locations will measure different properties, including different source sizes, source positions, and intensities. However, it is not known if measurements of the decay time of solar radio bursts are also affected by the observer's position. Decay times are dominated by scattering effects and so are frequently used to estimate the level of density fluctuations in the heliosphere, making any necessary location-related correction crucial. We use multi-spacecraft observations of interplanetary Type III bursts to investigate the dependence of both the decay- and rise-time measurements on the separation of the observer from the source. Using an improved fitting of the radio light curves, we determine that the decay and rise times are independent of the observer's position, identifying them as the only properties to remain unaffected. Moreover, we examine the ratio between the rise and decay times, finding that it does not depend on the frequency. Therefore, we provide the first evidence that the rise time is also dominated by scattering effects, adding to our understanding of the plasma emission process.