Hi,
To create the histogram regions right click the component and open the Component Properties. Under the Histogram tab you can specify the different region areas. Attached is a modified version of your project with one region defined.
I don’t see a large difference between the eye diagrams, only the Q factor. But since the Q factors are already so large the difference might just be due to the randomness of noise and the fact that the bit sequence length is short.
Cheers