Offchurch, Ledecestrescire. Southwest of Alcestre Monastery and Northeast of Evesham Abbey. Enemies are spaced out enough to whistle them into brush and pick them off or if you have chain unlocked the axe throw kills count as well and make it even easier. Noticed I had 8 in a row on that achievement earlier. Failed to get 8 or more by being spotted here. Tried again and got it first retry since I knew where enemies were