I'm a little unsure about the consequence of this change and I wonder if the intention is clear enough from the name of the new option. From the description, I understood you want to overlay lines for including the signal in the ratio plot, but from the implementation I think you still only have one line but that now includes the signal in the sum on the background. I think the change is ok otherwise, but I'd like to confirm this first...

The idea is to be able to include signal when calculating the data/MC ratio (i.e., data/S+B instead of just data/B). It's only necessary in specific use cases, like making post-fit plots from a S+B background fit (i.e., if the background doesn't describe your data fully, then signal plugs the gap to some extent) where it's more informative for the ratio to be data/S+B.

I don't need any extra lines or anything like that. Well, the ability to display two ratios (i.e., pre-fit and post-fit data/MC) would be good, but that's a different thing.