<p>The complex spectrum of non-Hermitian topological systems manifests extreme sensitivity to boundary perturbations when the system size is large. Hence, despite precise manipulation of non-Hermitian boundaries and sizes remains a challenge, it is of fundamental importance in developing ultra-sensitive sensing devices. Here, we address this issue using a non-Hermitian static mechanical lattice platform, with the lower bound of the accessible boundary perturbation being 10⁻²², about tens of orders of magnitude better than current systems, for a maximal size exceeding 10². This performance facilitates the exploration of various extreme non-Hermitian phenomena. As a proof of concept, we demonstrate theoretically the braid topology of non-Hermitian non-Bloch bands, whose sensitivity increases exponentially with the size. Based on the static platform, we measure experimentally ultra-sensitive braid phase transitions. Our study unveils the nontrivial interplay among non-Hermiticity, braid topology, and spectral sensitivity, and reaches a much improved level of controllable non-Hermitian boundaries and sizes.</p>