Having read the website, maybe I'm wrong. If you treat space as just another character, and they say it is then by far the most commonly used, you want that near the middle. As you are dealing with 27 characters, you're pretty much forced into a 6x5 grid.
If you allowed the keys to have non-standard widths you could add a 3rd space button between N and E. i.e. 1 1/3 width space, N, 1 1/3 width space, E, 1 1/3 width space. Might work on an on-screen keyboard, not so easy on a physical one though.