No surprise there. The huge westward null is due to a high ridgeline northwest of the city - the signal ain't going no further than the ridge anyway, so there's no sense trying to throw additional signal that way. The pattern follows the terrain northward and southward, and crosses low ridges eastward. Dayton to the north and NW Georgia to the south should benefit. The eastward lobe should really improve coverage in Cleveland and Bradley County.
I'll be in Cleveland the last weekend of July, so I'll be able to see what improvement there is, if any. Last time I was there in May 2009, I couldn't get many strong signals at all - I had to go to downtown Chattanooga to pick up all the stations. But that was before the transition ended for full-power stations.