I've always had expat contracts with net amounts: the company pays the tax and I know what I eventually will have "in my pocket" for spending in the host country. For an average expat it is almost impossible to understand what his nett pay will be if you are only discussing/negotiating gross amounts.

Cost of living index is another one of those expat typical confusing factors. (a friend of mine was given a 50% raise but then sent to a host country with a twice as high cost of living index as his home country )