< aññissa.m would be correct if it was
similarly declined as the demonstrative pronoum ima. >
Yes. This is actually the case. añña f. loc. is inflected like ayam, cf. f.
loc. imissa.m. It was noticed by the Pali grammarians. See Kaccayana sutta
63.
< Having bathed in another tank, one man entered the city in the eastern
direction. >