Let Q(z, w) = − ∏n k=1[(z − ak)(w̄ − āk) − R]. The main result of the paper states that in the case when the nodes aj are situated at the vertices of a regular n-gon inscribed in the unit circle, the matrix Q(ai, aj) is positive definite if and only if R < ρn, where z = 2ρ 2 n − 1 is the smallest 6= −1 zero of the Jacobi polynomial Pn−2ν,−1 ν (z), ν = [n/2].