If you are trying to get him to stride a little more open, try having his glove during E&O be further open. In other words, keep the shoulder/torso positioning the same but have the glove arm a little more open. I like to think of the tip of my glove pointing to the target.
It is difficult to stride more open without also changing something with the upper body to balance the body so maybe if he can focus on something other than striding but will result in a more open stride (such as the glove arm), the delivery will be more comfortable. The legs are large and fickle things :?
(I didn’t watch the video since I can’t right now but I will tomorrow. If this doesn’t seem like it would help, disregard it.)