This video presentation on attacking Zone 2 (middle of the field) with tunnel screens is with Coach Jason Ronquillo, Head Coach at Yelm High School (WA).
You can see the entire video and thousands of other coaching resources at Glazier Drive
The chart below shows the Yelm receiver identification terminology.
The X, Z, and C are the receivers on the left. X is the furthest receive to the left (closest receiver to the sideline), Z is next from left, C is closest to the ball--if there are three recievers on the left side.
On the right hand side, the furthest to the right (closest to the sideline) is Y, Z, is next from right, and C is closest to the ball--if there are three receivers on the right side.
When the name is called, that is the receiver who will be thrown to and the other receivers have blocking responsibility.
In the Yelm offensive system, the Running Back plays an H Back, and if the Quarterback is lined up in the pistol, the Running Back is in the Tailback position, signified by T.
Coach Ronquillo's "check back" series is called at the line of scrimmage by reading the defense and then calling the screen based on that read.
Watch the video below to see a discussion with diagrams and a live game film example of the Xavier screen--including the blocking responsibilities for linemen and skill positions. Both 3 x 1 and 2 x 2 receiver aligments are illustrated.
One of Coach Ronquillo's points of emphasis for screens is to not block linemen to the ground because when they get up, they are in a position to make a play on the screen. He would rather have a D Lineman retrace and recognize the screen because once they get up field, it still takes them time to get back to the ball carrier.