The SG may need a setting set , I don't know , I hear they are not so useful for diesels, so I did not buy one. I think idle load is more like 10% , just to get the Girl spinning.
Here is a diesel generator load chart and accompany fuel economy
You do not get something for nothing so you pay for load and rpm.
The way it reads is 50% load is the more efficient load.
http://www.wpowerproducts.com/wp-con...tion-chart.pdf
Diesel Fuel Consumption Chart | Worldwide Power Products