  We obtain stringent bounds in the
  < r^2 >_S^{K pi}-c plane where these are the scalar radius and the curvature
parameters of the scalar pi K form factor respectively using analyticity and
dispersion relation constraints, the knowledge of the form factor from the
well-known Callan-Treiman point m_K^2-m_pi^2, as well as at m_pi^2-m_K^2 which
we call the second Callan-Treiman point. The central values of these parameters
from a recent determination are accomodated in the allowed region provided the
higher loop corrections to the value of the form factor at the second
Callan-Treiman point reduce the one-loop result by about 3% with F_K/F_pi=1.21.
Such a variation in magnitude at the second Callan-Treiman point yields 0.12
fm^2 \lesssim < r^2>_S^{K pi} \lesssim 0.21 fm^2 and 0.56 GeV^{-4} \lesssim c
\lesssim 1.47 GeV^{-4} and a strong correlation between them. A smaller value
of F_K/F_pi shifts both bounds to lower values.
