I'm answering this much for myself as for others because some of the figures are counter-intuitive.

If NSW rake is 16% why does the AusTote premium show as ~19%?

Because the expected ratio is calculated as 100/(100-16) = 100/84 = 1.190

Worst case you only get 95% of that = 1.131.

So that leaves you ~13% better off.

But if you bet at least 20 minutes before the worst rake is 3.5%.

And that in theory leaves you 14.9% better off.

In practice it looks as if shorties aren't all that far below that but roughies give you a nice spice bonus.