I am not great at FAN's, but to me I use it to show that the human form can be abstracted to a thousand nuanced shades of grey when strategically lit.
I am not the greatest at the 'full on' approach. I consider that more glamour, whether there is clothing involved or not, where the subject's eyes drill into yours, the viewer.
In terms of discussing the subject with potential models I use the following text to aid the conversation and create common reference points for discussion:
If you don’t know quite how to describe what you want, you may find the following listing and discussions handy. There are no official terms, and there can always be some blurring between categories. This list of definitions, cast from the models perspective, can be used to help clarify the various forms of “nude” posing.
1. Implied Nude: I will allow you to make images with me which don’t show any clothing that I am actually wearing, implying that I am not wearing any.
2. Hidden or Covered Nude: I will allow you to make images with me not wearing any actual clothing, but with some sort of opaque drape or prop (possibly including my limbs) covering my private areas.
3. Sheer: I will make images with you in which private areas are somewhat visible through a translucent material, or out of focus or obscured by shadow. The opacity of the material is negotiable.
4. Semi-nude: I will make images with you of me in which my breasts and possibly my behind are visible at the same time as my face. Example: Early Playboy Magazine.
5. Artistic Nude: I will make images with you of me while I am not wearing any clothes if they are interestingly framed, strangely posed, or oddly lighted so as to not look like just pictures of me not wearing any clothes.
6. Figure Nude or Figure Study: I will make images with you of me in direct lighting while I am not wearing any clothes, but my expression will be neutral and I will be wearing little or no makeup so as to make clear that this is a figure study and not meant to be provocative, erotic, or otherwise non-serious.
7. Nude or Casual Nude: I will make images with you where I am casually posed, with full-body pictures made of me in direct lighting while I am not wearing any clothes.
8. Erotic nude: I will make images with you where I will assume provocative expressions and allow you to take pictures which draw particular attention to my private parts while I am not wearing any clothes. Example: Modern Playboy Magazine. I am not a fan of this but will work with you if this is what you want.
9. Adult nude: I will assume sexually explicit poses and allow you to take pictures of me engaging, or suggesting that I am about to engage, in a sexual act action while I am not wearing any clothes. I will not make Adult Nude images.