You forgot that coal is priced in US$ thus coal becoming cheaper...

You forgot that coal is priced in US$ thus coal becoming cheaper for buyers (or for the same local currancies, can buy more coal)

NHC can more than offset increasing A$ with increase vol through its port and incrase in quantity

What Macquarie say about A$:

"The A$ has traditionally been highly correlated with economic growth, which leads to stronger demand for commodities. The A$ is positively correlated with the OCED+6 leading indicator (LI), which is a strong proxy for the outlook for global production and economic growth.
For those internationally orientated stocks with low economic sensitivity, earnings are the most at risk. For these, there is no offset to the currency movement, particularly during times of strong A$ appreciation, which in turn reflects the view of a strong cyclical upswing in global growth – as at present.
Accordingly, during these times of strong A$ appreciation there are real winners such as resources (eg NHC due to port & coal export)