  The drastic rise of the proton structure function $F_2(x,Q^2)$ when the
Bj\"orken variable $x$ decreases, seen at HERA for a large span of $Q^2$, may
be damped when $x\to 0$ and $Q^2$ increases beyond $\sim$ several hundreds \g2.
This phenomenon observed in the Regge type models is discussed in terms of the
effective Pomeron intercept and of the derivative $B_x=\partial{\ell n
F_2(x,Q^2)}/\partial{\ell n(1/x)}$. The method of the overlapping bins is used
to extract the derivatives $B_x$ and $B_Q=\partial{\ell n
F_2(x,Q^2)}/\partial{Q^2}$ from the data on $F_2$ for $6.0\cdot 10^{-5}\le x\le
0.61$ and $1.2 \le Q^2$ (\g2) $\le 5000$. It is shown that the extracted
derivatives are well described by recent Regge models with the Pomeron
intercept equal one.
