  Inverse techniques are used to extract information about an exoplanet's
atmosphere. These techniques are prone to biased results if the appropriate
forward model is not used. One assumption used in a forward model is to assume
that the radius of the planet is constant with wavelength, however a more
realistic assumption is that the photospheric radius varies with each
wavelength. We explore the bias induced when attempting to extract the
molecular abundance from an emission spectrum which was generated with a
variable radius. We find that for low gravity planets, the retrieval model is
not able to fit the data if a constant radius model is used. We find that
biased results are obtained when studying a typical hot Jupiter in the MIRI LRS
wavelength range. Finally, we show that high gravity planets do not suffer a
bias. We recommend that future spectral retrievals that interpret exoplanet
emission spectra should take into account a variable radius.
