When restricted to proving $\Sigma _{i}^{q}$ formulas, the quantified propositional proof system $G_{i}^{\ast}$ is closely related to the $\Sigma _{i}^{b}$ theorems of Buss's theory $S_{2}^{i}$ . Namely, $G_{i}^{\ast}$ has polynomial-size proofs of the translations of theorems of $S_{2}^{i}$ , and $S_{2}^{i}$ proves that $G_{i}^{\ast}$ is sound. However, little is known about $G_{i}^{\ast}$ when proving more complex formulas. In this paper, we prove a witnessing theorem for $G_{i}^{\ast}$ similar in style to the KPT witnessing theorem for $T_{2}^{i}$ . This witnessing theorem (...) is then used to show that $S_{2}^{i}$ proves $G_{i}^{\ast}$ is sound with respect to $\Sigma _{i+1}^{q}$ formulas. Note that unless the polynomial-time hierarchy collapses $S_{2}^{i}$ is the weakest theory in the s₂ hierarchy for which this is true. The witnessing theorem is also used to show that $G_{i}^{\ast}$ is p-equivalent to a quantified version of extended-Frege for prenex formulas. This is followed by a proof that Gi p-simulates $G_{i+1}^{\ast}$ with respect to all quantified propositional formulas. We finish by proving that S₂ can be axiomatized by $S_{2}^{1}$ plus axioms stating that the cut-free version of $G_{0}^{\ast}$ is sound. All together this shows that connection between $G_{i}^{\ast}$ and $S_{2}^{i}$ does not extend to more complex formulas. (shrink)