If the journey is simply 200 ri (100 ri plus 100 ri) from Ito, ending up in the state of Fumi (possibly near today's Osumi Peninsula), to then travel south by sea for 10 days would mean that Yamatai is located in the Pacific Ocean, past the Japanese islands.
そこから単純に100里+100里＝200里が不弥国（大隅半島付近？）と考えると、さらに10日南に水行する邪馬台国なるものは日本列島を飛び越えて太平洋上になってしまう。