Based on your paper, it seems you didn't compare to other model based evaluation method such as Frechet Embedding Distance (FED). I would certainly like to see correlation study between each model evaluation method.
Thanks for your feedback, while we couldn't compare with all model-based methods out there, YiSi (August 2019) and BERTScore which was just presented at ICLR2020 this week (April 27th 2020) are very strong methods to compare against and reflect state-of-the-art. All comparisons are welcome!