I used to tie the wing on an X-caddis like the wing on an EHC. I now tie the wing a bit shorter on an X-caddis.
I've talked to Craig Mathews about the X-caddis. Craig Mathews explained that the X-caddis has a shorter wing than the EHC. He says that you can tie it as long as the shuck but I do not. It is an emerging wing. I can't prove it, but I personally think that a shorter wing indicates an insect in an earlier stage and more vulnerable to the fish. So if you are going to make a mistake in wing length, better to it tie it a bit shorter rather than longer.
Take a look at the link to Dave Hughes book below and compare the wing length on the EHC (flies 1-4) in the photo to the X-caddis (flies 5-6) to see the difference.
Essential Trout Flies By Dave Hughes
In the video below Craig ties the wing as long as the body. Notice how short he clips the shuck.
Hans Weilenmann also does not tie the wing on his CDC and Elk beyond the hook bend.
"Discovery consists of seeing what everybody has seen and thinking what nobody has thought"..........Szent-Gyorgy