My initial perception is that the image as a whole doesn't look relatively sharp anywhere. That could have to do with the down-sampling for inclusion into the galleries, or possibly affects of diffraction.
At f/20 you are well into diffraction on a DX sensor. If you were shooting a macro image, I might agree that a trade off of a small loss in fine detail would be offset by the gain in DOF. But it usually is not a good idea with landscape images. I wouldn't have gone beyond f/11. At f/11 and 18mm with a 5 foot focus distance you would have had a DOF from about 2.5 feet to infinity.
And to that point, you need to decide what the main subject is. Some people would use the hyper focal distance to get the maximum DOF. But if the background is more important to the image, some would argue that that should be the plane of focus. You only loose a bit of foreground DOF, but gain more relative sharpness where the subject is.