We present a new method to enhance multi-mono coding of ambisonic audio signals. In multi-mono coding, each component is represented independently by a mono core codec, this may introduce strong spatial artifacts. The proposed method is based on the correction of spatial images derived from the sound-field power map of original and degraded ambisonic signals. The correction metadata is transmitted as side information to restore the spatial image by post-processing. The performance of the proposed method is compared against naive multi-mono coding (with no side information) at the same overall bitrate. Experimental results are provided for the case of First-Order Ambisonic (FOA) signals and two mono core codecs: EVS and Opus. The proposed method is shown to provide on average some audio quality improvement for both core codecs. ANOVA results are provided as a complementary analysis. Index Terms-ambisonics, audio coding, spatial audio.