Well yeah, otherwise the inside channel would be far too crowded, you couldn't have an inverted wing back and an inside forward/inverted winger working together, they'd end up occupying the same space, which is why I was curious about playing narrow with inside forwards and an AP, thought it could all get a bit crowded in there. IWBs and W's seems like a pretty well balanced and logical set-up to me, not one I'd use personally, as I like my wingers to get inside and try and get goals, and get my width from attacking wing backs, but no reason why it wouldn't work if you had the right players.
As I said I tend to have one Winger and one Inverted Winger - at the moment I have my Winger on the right (usually Buendia), and Max Aarons behind him in a WB(s) role. But maybe I should try him as an IWB and see how that goes. Third season he should be good enough to contribute quite well to the deeper midfield area I should think.