My (not very scientific) reasoning behind the difference between Fenugreek on an empty/full stomach is that on an empty stomach, it just gets burned by the body for energy - on a full stomach, the body has a chance to make optimal usage of the fenugreek (maybe as a hormonal precursor).
I've eaten Fenugreek curries - many Indian restaurants will sell you Aloo Methi (Methi=Fenugreek), but I've never tried a Fenugreek soup! It's been a popular food ingredient in Eastern countries for thousands of years, apparently, as well as being regarded as a medicine.