+ O\left(\frac{1}{Q^2}\right)\right]\ 
\nonumber \\
&\equiv & D_A^{(0)}\left[\, 1 + O\left(\frac{1}{Q^2}\right)\right]\ , 
\label{D0}\end{aligned}$$ where $\mu$ is the factorization and/or renormalization scale, $\phi_{a/A}(x,\mu^2)$ is the leading twist parton distribution of flavor $a$ in a nucleus normalized by the atomic weight $A$, and $d\hat{\sigma}^{(0)}_{ea\rightarrow eX}/dx_B dQ^2$ is a perturbatively calculable short-distance hard part, which is independent of the nuclear medium. The [*total*]{} DIS cross section normalized by the atomic weight $A$ is an inclusive quantity and depends only on one hard scale $Q^2$. The QCD factorization theorem [@CFP; @Ellis] allows us to factorize each term in Eq. (\[D0\]) into a convolution of a short-distance coefficient function and a corresponding matrix element. The $1/Q^2$ term in Eq. (\[D0\]) can be expressed in terms of twist-4 matrix elements [@Ellis]. As demonstrated in Refs. [@QS_fac; @Qiu], integration of all position variables ($y_i$) of the field operators, which define these twist-4 matrix elements, are bounded by $1/x_Bp$ due to the oscillating exponential. Let $m$ and $r$ be nucleon mass and radius, respectively. If $1/x_Bp < 2r(m/p)$ (i.e. $x_B > 1/2mr \approx 0.1$), all the fields in these twist-4 matrix elements are bounded within the size of individual nucleon. Therefore, the power suppressed terms in Eq. (\[D0\]) is 