This is somewhat similar to a post of other's from yesterday, which pointed to the difference between females of P. agna and mathias, as in the placement of the 1b spot. Unfortunately the 1b spot is not visible on this individual, although there's a good underside shot of both wings.
Kimura states that the forewing spots on agna are larger, though this is not particularly obvious on specimens on Yutaka.

My feeling is that this is agna, but would appreciate some comments or confirmation.
Photographed October, Nan province, forest at 425 metres.
With thanks.

b8265 Bengal Swift (Pelopidas agna agna) 425 m - Huai Rong 01.JPG

b8265 Bengal Swift (Pelopidas agna agna) 425 m - Huai Rong 02.JPG