I swapped to a flatter saddle that I had lying around today (Prologo Nago Evo) and the lower back rounding was almost completely gone.
I want to ask fellow Specialized users what their experience in swapping widths between the Romin and Toupe. I used to be on a 155 Toupe, which I found a tad wide and I was just on a 143 Romin. I've been told that the Romin actually runs a size bigger than the corresponding Toupe, but never found any definitive answer on this.
Also, which saddles have a similar profile to the Toupe? Not just flat, but similar curviture? The Prologo that I'm on doesn't support me very well and I want to consider other options before I get another Toupe.
I currently have a 143mm Toupe on one bike and 143mm Romin on another, and they feel similar width-wise. For me, the main difference between the two is that the Romin feels more comfortable when I am in the drops.
One non-Specialized saddle that I have had a good experience with was the Bontrager Inform RXL in 146mm width. It is somewhat flat but drops off a bit on the sides, and it seemed to provide good support although not as comfy as the Romin while in the drops.