Alef:
There seem to be several reasons why F/M-stories are inherently different from M/F-stories, most of them having to do with the ways we perceive men and women. Here are a few:
1. The idea of a man (often big and strong) being dominated by a woman (often petite) seems to be erotically charged in itself - to the degree that some of the stories seem to have this situation as its only point of departure.
2. Dominatrix-stories play on female sexuality in a way that a story with a male Dom cannot replicate.
3. A number of stories in the challenge have plots where a group of women gang up on a man to give him a good spanking (often his wife and her best friends). It's possible to imagine a role reversal where a group of men gang up on a woman, but it would have to be written with great care to avoid an unpleasant feeling of assault. In addition, it's a plot that would probably fail to appeal to most men as they would have a feeling that they should be able to deal with their wife on their own. There are definitely fantasies and stories where a woman is spanked by several men, but I think they tend to be more exotic, as stories about women abducted by a group of soldiers or pirates, or kept hostage by a primitive tribe.
Here's my take on these aspects as a 'bottomish' male who tends to identify strongly with the spanked masculine characters in F/M stories:
[1] Yes, I find the idea of a bigger, stronger male who submits to being corporally corrected by a female who has no hold to compel such cooperation other than their respective natures--perhaps he's made an agreement, verbal or even written, to do so, but making such an arrangement would be based on him voluntarily agreeing to cooperate in being punished that way--to be strongly compelling.
If the story is written convincingly, once the feminine disciplinarian has pronounced sentence on the male, whether the spanking is truly deserved or not, I'll be figuring, "Well, he's sunk now, there's no way he's getting out of this situation without a sore seat." He might argue, beg, promise reform, protest and/or stall, but his behind is ultimately going to be blistered, and I never say to myself that "Hey, he could just say 'no' and walk away." Psychologically it just doesn't work that way, thus he'll accept his corporal correction, albeit rather grudgingly in some cases.
[2] I suppose that's so, I'm not much 'into' stories featuring dominatrices myself.
[3] Part of this appeal likely relates to #1 above, because the male spankee may be easier to control if he's outnumbered by the females involved in punishing him, whether as spankers, facilitators and/or merely witnesses to his walloping. To me, in appealing F/M accounts dealing with this favored plot device, the outnumbering factor is more important in a psychological sense than a physical one, helping convince the masculine victim that his feminine chastisers, by all being in agreement together, must therefore be correct in their actions and beliefs, thus he must deserve the intensity of the discipline he's undergoing.
Of course, the presence of multiple disciplinary females almost always heightens the embarrassment effect as well, I'd venture, especially if they're teasing the hapless male, plus notably if he's experiencing some degree of nudity during his spanking session.
Another literary aspect which I associate primarily with feminine chastisers is the employment of light-hearted, breezy dialogue, especially if the actual punitive session is quite extended and/or intensive--I greatly enjoy the contrast between a lightly playful verbal approach and a highly hurtful physical one, with the females bantering and chattering cheerily as they administer extremely strenuous corporal correction...
--C.K.