Nicely Carved Small Wooden Mask, Unknown Origin

I haven't been able to definitively determine the origins of this small, nicely carved mask, which I purchased from the estate of an artist and collector and world traveller near me--the closest match I can find, distinguished by the raised rims around the eyes and mouth, is Ngbaka, from the Democratic Republic of Congo. (reference photo included.) This one is of small scale, too small to be worn, but what wonderful carving of those eyes and mouth and nostrils of the nose and especially what I take as ears laying flat to the sides. 

5 1/8" x 3 1/2" and in very good condition, nice warm patina, with what appears to be a fair bit of age to it.