# Size of output and post selection registers

Let $$\mathcal{A} =\{\mathsf{Q}_n\}$$ be a quantum circuit, taking $$n$$ input qubits to $$n$$ output qubits. It is known that $$$$\mathsf{Post}\mathcal{A} = \mathsf{Post}\mathsf{BQP},$$$$ where $$\mathsf{Post}\mathsf{BQP}$$ is defined here.

Without losing any generality, could I say that the output register of every circuit in $$\mathsf{Post}\mathcal{A}$$ is a single qubit, and the post-selection register of every circuit in $$\mathsf{Post}\mathcal{A}$$ has $$(n-1)$$ qubits?

Note that the output register is always a single qubit, but it wasn't immediately clear to me how much we can tweak the size of the post-selection register.