Oh I see, thanks. I have seen those, just didn't think of it - they seem strictly worse than two separate halves to me, the main thing that appeals to me (I don't have one) is positioning either have however, at whatever angle, and differently to the other, to suit me and how I happen to be sitting at the time. Split segment seems to make a big assumption about what people find uncomfortable (narrow/er than shoulders) and offer a different fixed solution.