The fat you are referring to as "behind the abs" is visceral fat. Organ fat. It's harder to get rid of in the sense that you will primarily lose subcutaneous fat first. It's been said that stress and in turn cortisol lead to more storage of visceral fat.. (VAT). In reality they are the same types of fat, (white adipose tissue) just deposited differently.
The real two distinct types of fat are white adipose (WAT) and brown adipose (BAT). That's a whole other subject.