Is your antenna height on the chimney really going to be 10'? It would be interesting to run another report at the maximum height you figure you can mount your antenna. If you use a chimney mount, you can buy a 10.5' chain link top rail cheap at the local home center and use that for your mast. Should give you 5' or so above the chimney top.
You have a fairly easy distribution of stations, as you have noted. KNTV real channel 12 is a VHF high station, which your little antenna should be much less sensitive to than the UHF stations. KGO 7 is also VHF high, but maybe you can see it because it's stronger. A sensitive VHF antenna will be long/large, to catch the comparatively long wavelength of the VHF band.
If you want to keep things simple, how about one of the HBU series antennas from Antennacraft?
http://www.antennacraft.net/Antennas/AntennasHBU.html I would expect that even the HBU11 on a mast would pick up more stations than the Mohu at ground level, and as you go up in size, the antennas sensitivity will increase.
Be sure to pick your antenna location so that it is not obstructed by trees or neighboring buildings in the path of the stations you want.
