Not basin. Border on Amur instead of buffer zone. Left bank IS possible, but nothing more than this. And it was possible to give up left bank, just like China gave up Baikal Lake area in 1670ies - prestige holdings.
But that will tie hands of Russia in dealing with steppe people even more than OTL Nerchinsk and Kyakhta treaties. As Chinese bank will ALWAYS have better garrisons and fortresses (ALWAYS = during the entirety of 18th century).
But that will tie hands of Russia in dealing with steppe people even more than OTL Nerchinsk and Kyakhta treaties. As Chinese bank will ALWAYS have better garrisons and fortresses (ALWAYS = during the entirety of 18th century).