  In this paper, we investigate the variance of the nodal length for
band-limited spherical random waves. When the frequency window includes a
number of eigenfunctions that grows linearly, the variance of the nodal length
is linear with respect to the frequency, while it is logarithmic when a single
eigenfunction is considered. Then, it is natural to conjecture that there
exists a smooth transition with respect to the number of eigenfunctions in the
frequency window; however, we show here that the asymptotic variance is
logarithmic whenever this number grows sublinearly, so that the window
"shrinks". The result is achieved by exploiting the Christoffel-Darboux formula
to establish the covariance function of the field and its first and second
derivatives. This allows us to compute the two-point correlation function at
high frequency and then to derive the asymptotic behaviour of the variance.
