We investigate the structure of the moduli space of 9D heterotic interpolating models with a complete set of Wilson line backgrounds and a radius parameter by computing the one-loop partition functions and the cosmological constants and by deriving the massless spectra, paying attention to the region where supersymmetry is asymptotically restoring. We find some special planes and points in the moduli space where the gauge symmetry is enhanced and/or massless fermions appear. The gauge symmetry is maximally enhanced at the minima of the one-loop effective potential where the cosmological constant is negative.