It was recently demonstrated that in planar geometry, the classic P(N)
equations are an asymptotic limit of the transport equation. A corres
ponding boundary layer analysis established the asymptotically consist
ent boundary conditions. These boundary conditions were evaluated vari
ationally, and it was conjectured that these variational approximation
s are quite accurate for all values of N. Here, we evaluate these boun
dary conditions exactly (numerically) and show that the previous varia
tional results are indeed accurate to a few percent. The exact results
were computed using numerical methods previously developed for solvin
g Chandrasekhar's H equations.