Amans, who appears in the Vulgate and is probably to be identified with Malory’s King Aniause, took advantage of the war between Arthur, Ryons, and the Sesnes to attack Carmelide.
Thus, Amans’ land would most likely have bordered Cameliard. Since the area south of Cameliard is Bertilak de Hautdesert’s territory, and Bertilak seems to be more or less allied with the powerful Morgan le Fay, I would put King Amans’ land north of Cameliard, between about the Mersey River in the south to about the mouth of the Ribble River (at Preston) in the north.
Knowing no other name for this territory, Phyllis Ann Karr use the name of it’s king, as do I.
See also
Amans’ Daughters | The Legend of King Arthur