It doesn't let his head go al the way up in bot mode unless you unlatch his back (a little) Here's what he normally looks like:

Now, you'll notice it sits pretty low, even by Soundwave standards. BUT. If you take the cone on the back of his alt/bot mode:

open it

POP IT OFF

Turn it around, and re-connect it, then fold it in. The result is a Prime Soundwave with a much better and more posable head!

Also it covers up the back end of his vehicle mode even better than before!

Hope this helps!