DoF doesnt quite work like that actually (speaking as a photo journo). While it will increase by moving further away from your subject you will actually lose more depth of field by zooming in again than you gain from moving the camera back. Best way to gain DoF is to use a narrower apeture. Look in the setting of your camera, i would go for F11 on something like this TBH, F8 is usually enough for single miniatures.
As for comments on the diarama, its a good effort, Boris looks a bit relaxed, i know Heresy do some more dynamic poses which may suit more. And the walls look a little flat, they need more texture. The zombie pool thing looks really cool though.
One problem you have is depth of field - the length of the region that's in focus. Close up, only a thin slice of the air is in sharp focus (in this photo, just the back wall, which is what your auto-focus beam was probably hitting). You can get a better depth of field by moving your camera further away from the target. See http://www.mir.com.my/rb/photography/fototech/htmls/depth.html
This is a great piece, which is even better in real life. The photo just doesn't do it justice.
The only comment I made to Karnage when seeing it, was that the rear wall should have been on the near side of this piece (as we look at it in this photo.)
The viewer would have been looking at it from Boris's perspective then, over his shoulder, which IMHO would have been more effective.
Great use of all the mini's concerned and quite evocative of Boris being not at all fazed by what he has encountered :)
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