This document explains the rationale behind the final changes that were incorporated into the Domain 1 MPA proposal as it was presented to CCAMLR 38 in 2019 (CCAMLR 38- BG/22; SC-CAMLR 38-BG/03). Those changes were then based on the most recent publications, on WG-EMM discussions as well as documents regarding a krill fishery management workplan, and suggestions made during the 2018-2019 intersessional discussions after the D1MPA proposal was formally introduced by Chile and Argentina at CCAMLR 37. The document also addressed the outstanding issues as raised by Members during the SC-CCAMLR 37 Meeting in 2018. This document once again provides detailed information about the rationale behind the modifications included in the D1MPA model, in such a manner that conservation objectives are achieved, while allowing for the fishery to redistribute and avoid further spatio-temporal concentration. The specific changes made to the D1MPA model are described. Since the initial presentation, both Argentina and Chile have been openly available to engage with interested Members so as to address any outstanding concerns. Both Members are nonetheless of the view that the proposal's solid scientific foundations are sufficient for the proposal to be presented for the Commission's consideration in 2020.