You have a lot of signal in the air. I would conclude that the building is shielding your antenna.
The makeup of the building and its surrounding buildings and trees makes a big difference to how much signal is available. The TVFool report assumes a clear-air installation; its a simulation that does not account for obstructions like buildings or trees.
Any chance you can mount an antenna outdoors on your roof? That's the best response to your situation. If you have a balcony or window that faces the direction of the signals that you want, you could try locating the antenna there. You could install a modest antenna on your roof, unobstructed by trees and buildings, that would receive many stations.
I don't think much will change by trying different antennas indoors. Whatever your building is made of, or the surrounding buildings, is likely shielding you from the signal. Get a long cable and take the antenna outdoors as high as possible, and see what changes.
Here's a page with some basics about siting an antenna -
http://www.hdtvprimer.com/antennas/siting.html - regard the section about trees.