Lookback Chiwoo Eye Size

Hi! I got the Feeple60 Lookback Chiwoo in tan because the Chiwoo is like potato chips, you can't just have one. That being said the head IS quite a bit smaller than the original Chiwoo head. The original wears 18mm eyes but those are far too big for the new boy. Does anyone know what size fits this beautiful boy best?

Thank you!!!
♡Mini