Inversions- Persian Gulf
Out of Dubai & Bahrain we used to not derate under any circumstances & make an educated guess at the temp in the inversion. F/E would note the EPR for this temp & go to this EPR (or near it) as soon as the inversion was encountered,then fine tune for actual temp. Inversion usually kicked in around 400 -600 feet.
It seemed that the later at night the stronger the inversion,which figures. Sharpest I remember was about +15 degrees out of Bahrain at 0400 local. Technique where you did not have 100 miles of clearway in the event of EFOT/O would be another matter.