I don't believe in the BMI, first of all, because everybody's body is different. It doesn't take into account frame or muscle mass or body fat-percentage and fat distribution (the latter two which are the most important indicators of health).
To me, it's all about how a person carries their weight. Fat can be someone who is only mildly overweight but the extra weight doesn't match their frame. Conversely, someone can be moderately overweight and still look pretty darn good.
It all comes down to aesthetics and depends on the person and how their mass either enhances or deters from their appearance. I don't think there's any way anyone can sit down and give a universal indicator of what they consider fat or what they consider just right.... at least where attraction is concerned.
If you look good, you look good. Regardless of whatever number shows up on the scale or where on the BMI or WHR you fall into.
That's just my take on it.