Orange- I'm going to go overkill on this just because I think its an interesting question. Here are 2 diagrams where I am asusming the server stays back. I've got the net person with a range of 10 feet and the back person with a range of 30 feet since they get to let the ball bounce. Here is with the Net person pretty much in the middle of the box where you had them in that original diagram.
I think that is a VERY easy return with that much baseline available. Again- thats a full 1/3 of the baseline...
Here is the court coverage for where I think the net person should be set up on the return of serve when the ball is wide.
On a wide serve I think the net person should probably have one foot in the alley.
You can pick different numbers for how much range you think that a net person or the baseline person has. 10 feet and 30 feet I thought was pretty reasonable.
To see how my assumptions look when serving up the middle here you go.
That looks about right to me when the net player is set up in an aggressive position.