In this balningau thread, Ilmen suggested swapping x2 and x3:
{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:
• bongu-2: https://www.alexburka.com/~danr/#?stats_reduce=word&cqp=[tags%20_%3D%20%22bongu2%22]&search_tab=1&hpp=100&search=cqp
• bongu-3: https://www.alexburka.com/~danr/#?stats_reduce=word&cqp=[tags%20_%3D%20%22bongu3%22]&search_tab=1&hpp=100&search=cqp
As you can see, there is five hits for bongu2 used as a body, and three hits for bongu3 used for the same purpose.
In this balningau thread, Ilmen suggested swapping x2 and x3: