Overseas pension policy deductions is always a hot topic, this area has been well reviewed by Susan St John and Dr Claire Dale.
A maze of issues and a rational approach often lacking.
Go back to 2013
http://docs.business.auckland.ac.nz/Doc/Proceedings-OS-Pensions-Forum-6-Jun2013.pdf
The current Government has done some minor tweaking around the edges, and finally the spousal issues has been addressed. One of the villains of the S70 pathway, has been the Ministry of Social Development , on this topic a culture of avoidance, lack of policy transparency and poor communication in place over many years. The last presentation by Ministry staff I listened too was poorly presented, with the speaker frightened of the possible audience response, not the way to approach a difficult topic. Like the rabbit in the car headlights! If a topic is difficult be up front as to why, use case studies to explain policy implementation, and seek from the audience potential answers. It often then becomes a shared issue, and all move forward.
A 2018 media statement might be of interest
Rob Stock article this week takes another look at the issues