{bongu} doesn't comply to the body part gismu family's argument structure: x1: body part, x2: body/individual (+ possibly a function argument x3)
{bongu} should parallels {rango}'s argument structure, and this is the way {bongu} is usually used, as evidenced by the results retrieved by korpora zei sisku:
In this balningau thread, Ilmen suggested swapping x2 and x3: