Australian regulations IFR ...
One needs to keep in mind that the OEI operational requirements in 20.7.4 hark back to the now-defunct airworthiness requirements of 101.22. Beware that, with the rubber stamping of foreign certifications, post Yates Report (from around 1990 or so), you just might see the foreign POH providing something less than the 20.7.4 operational requirement. Likewise the 6% AEO takeoff climb WAT requirement ....
Responsibility, I guess, lies with the PIC to do some sums and, where necessary, reduce the POH gross weight to satisfy 20.7.4 ?