I have touched briefly before on the whole "topping from the bottom" issue and I would just like to clarify my opinion on the topic. Some people get caught up on this and the implication is that anything the "sub" suggests is an attempt at topping. I see it differently.
If submissive B suggests to Domme A that by using the futon cushion, with the bean bag below, and the larger throw pillows under her bottom he will thereby have better access to her (whatever she wants attention paid to) and at the same time she will not have to support her body weight on her "feet-hands-elbows-knees-etc" then the purpose of his suggestion is to benefit them both in their mutual pleasure. Its not an attempt to switch roles, or his trying to become the boss, exert power, or to "objectify" her (or him if its a male Dom) in some fashion.
On that note, I have always felt that good sex involves at least *some* objectification, some domestic violence (not in the bad way as you all fully know) some slapping, biting, and some sort of humiliation. I mean seriously, Hollywood has long depicted "sex" as some sort of "1950s, Ward and June Cleaver, romantic kissing, soft music, dainty, sanitized type of act when in reality it usually seems to be "Harder, Harder, fuck me harder, spank this, twist that, suck it and swallow it" escapade.
To that end, if it appears that if a sub/slave is trying to "reverse roles" that does not mean they have some secret agenda to overthrow the Dommes rule. In my mind this is supposed to be fun. If someone has a good idea, or a better idea, or has more experience, or a bigger-faster-better toy, a new twist, a revised edition, a newly discovered position, and if it makes both people happier and satisfied, then it matters not one whit who suggested the idea.
The only case where this could be a major point of contention is if "Domme" wants/enjoys candle wax, golden showers and enemas, and "sub" enjoys St. Andrews Cross, single tail floggers, and has a foot fetish. In that regard they have probably no business being together or "playing" with each other and it doesn't matter who is the top or bottom, Domme or Sub, no one is going to be happy.
All of this kink and fetish that we do should be to make peoples lives happier, more exciting, and a mutually beneficial activity. Suggestions and ideas should be freely exchanged. At least in my opinion, though I could be wrong. :)
