OK. I was under the misimpression that this was a typical home or apartment, not a commercial building. So the actual signals are probably rather weaker than TVFool/RabbitEars predict.
In the previous thread he said WMAQ (on RF 29) was his "problem" signal. That's a somewhat weaker station according to the RabbitEars report, so once you attenuate it even more going through trees and two walls, you probably don't have much signal to work with.
It's a situation where you really need to get up on the roof, but being a commercial building, that's obviously not an option either.
This may be a situation requiring some creative thinking, perhaps ganging two DB2e's so each can be placed in a "hot spot." Of course once you do that, it can be pretty tricky ensuring the signals from both antennas stay in phase across the UHF band. And the best you get from two antennas is 3 dB extra. You may need four antennas (equivalent to a DB8e) to get enough gain - and then the phasing problem gets even touchier....
One last off-the-wall suggestion, though. Before sending the DB4e back, could he try tilting it? (Keeping the elements horizontal, of course.) I know that sounds crazy, but I'm thinking the signals are hitting the whole DB4e, but are out of phase - hence the worse performance. Perhaps the "hot zone" isn't vertical but instead is at some crazy skew within the room.
And even if that works, it may not be practical; but I'm just trying to get creative since no "ordinary" solution is likely to work (we're already trying outdoor antennas indoors).