Hi Bryan. There is no iron clad grip involved, quite the opposite in fact , sure the shape is retained but the fingers are quite relaxed. This may on the face of things seem difficult but in reality its fairly easy to slide up and down the neck once you know how.
Looking closely at that Y shape ( I call it the F chord shape) with the ring finger and pinkie on the two outer strings. I call these two strings ‘rails’ Take all the pressure off the strings whilst retaining contact with the strings slide the shape up the neck focusing on the positions of the ring finger and pinkie and using the rails to help guide you to stay on the track. This does take a bit of practice to master more so landing accurately at the C, D and back on the G locations. The secret is to take it slowly. check each finger position when you take off and land at each new location whist you memorise each location. With daily practice within a week or two you’ll have it nailed.
In the following lesson you’ll be taught how to make the X shape (I call this the D chord position) Here is a tip that will help you easily swap between the Y and X shapes.
Make the Y shape anywhere on the neck. For this ‘exercise’ it doesn’t matter where on the neck you do this just where you feel most comfortable.
Ok with the Y shape on the finger board look closely at the positions of the index and middle fingers. Keeping the Ring Finger and Pinkie firmly on the rails swap the positions of the index and middle fingers you are now in the X shape. It’s that easy.
Most students find the Y shape easy to make but struggle with the X shape. But if you make the Y shape first then practice flipping the index and middle fingers as I have explained you find it so much easier to learn the X shape (D chord shape) and later when you learn to slide up and down the neck moving between the Y & X shapes becomes second nature.
Remember if at any time your struggling to do something go back and review the lesson as many times as you need. Good luck