It's a wider duplex, that's about all there is to it.
I have wide duplex, duplex and heavy duplex reticles in FXII 4x33's on various rifles. The wide duplex differs primarily in that the duplex area covers less of the target thus allowing you a clearer sight picture.
On big targets up close I prefer heavy duplex; for targets further than about 200 yards I like wide duplex, for everything else there's regular duplex.
They all work, it's just splitting hairs really.