Being both an engineer and a pilot I find it quit amusing how heated the debate sometimes gets between the worlds of theory and practise.
Two years ago during a flight I got really worried because of an increase of oil temperature. For some time the engineer took over and I stopped flying the helo. Since then I made up my mind that on the ground I would be an engineer and in the air a pilot : in the green is in the green, point. That does not mean that on the ground an equally simplistic approach to the problem should be taken.
As far as ground effect is concerned there is a fair understanding of the effect, even quantitative. An attempt to over-cook this is useless. Some people in this thread stated 1 diameter is OGE and as a pilot I would say this is a good average decision point, as far there is no tail wind, and no unusual ground surface. As a pilot I also rather would monitor descent rates, tail wind and power settings instead of inches of skid hight (as I do not have a telemeter I probably would anyway make a very rough estimate). From there making the leap to stating : all that is not IGE is OGE is fair. But then consider the engineers view point : power needs are easier to calculate OGE than IGE (cfr my previous remarks). When doing tests constructors want a reference. The lower that is, probably the easier the tests are and the better the machine is going to look. So from that view point it is in the pilots interest the OGE does not get defined as too low.
So all together 1.5 skids above the ground is not all that bad. This weekend I played around with it: first low hover, then increase power a bit and let the helicopter bounce up and down until it settles. Keep on increasing the power untill you really take off (carefull for HV...). When doing the tests this rigourously I had the feeling that ground could be felt slightly higher than 1 diameter..