Your definition is flawed. Contraception is not a "way" of having sexual intercourse. Contraception is a frustration of one of the natural ends of marriage, namely, procreation. It can also have detrimental effects on the other end of marriage which is the unifying of a man and a woman in love. Contraception is an act AGAINST sexual intercourse rather than a method of it. 

Your assumption that NFP can be contraception is based on the idea that personal intention is the primary factor in determining a moral act. This is a faulty understanding of moral actions. I'll use an extreme example to demonstrate how such an approach plays out in reality. Many Americans claim that the dual atomic bombing of Japan in WWII in which thousands of young children (along with adults) were incinerated was a morally OK because we had the intention of saving millions of lives in the long run through a shortening of the war. This is wrong. Incinerating children is always wrong no matter the intention.