Let $({\mathfrak{V}},{\mathfrak{L}})$ be a ${K^{\circ}}$-model of $(V,L)$. Then ${\|\hskip 4.30554pt\|}_{\mathfrak{L}}$ is a semipositive formal metric if and only if ${\mathfrak{L}}$ is a nef formal ${K^{\circ}}$-model.