We describe along the guidelines of Kohn (Quantitative Estimates for Global Regularity. Analysis and Geometry in Several Complex Variables, pp. 97–128. Trend Math. Birkhauser, Boston, 1999), the constant \({\mathcal {E}}_s\) which is needed to control the commutator of a totally real vector field \(T_{{\mathcal {E}}}\) with \(\bar{\partial }^*\) in order to have \(H^s\) a-priori estimates for the Bergman projection \(B_k, k\ge q-1\), on a smooth \(q\)-convex domain \(D\subset \subset {\mathbb {C}}^{n}\). This statement, not explicit in Kohn (Quantitative Estimates for Global Regularity. Analysis and Geometry in Several Complex Variables, pp. 97–128. Trend Math. Birkhauser, Boston, 1999), yields regularity of \(B_k\) in specific Sobolev degree \(s\). Next, we refine the pseudodifferential calculus at the boundary in order to relate, for a defining function \(r\) of \(D\), the operators \((T^+)^{-\frac{\delta }{2}}\) and \((-r)^{\frac{\delta }{2}}\). We are thus able to extend to general degree \(k\ge 0\) of \(B_k\), the conclusion of (Quantitative Estimates for Global Regularity. Analysis and Geometry in Several Complex Variables, pp. 97–128. Trend Math. Birkhauser, Boston, 1999) which only holds for \(q=1\) and \(k=0\): if for the Diederich–Fornaess index \(\delta \) of \(D\), we have \((1-\delta )^{\frac{1}{2}}\le {\mathcal {E}}_s\), then \(B_k\) is \(H^s\)-regular.