You might lose the signal, since you'd be getting one signal direct and one off the side. Combining the two into one coax cable would essentially be the same as multipath.
Considering that as close as you are to South Mountain (you're still in Tempe, right?), even a slight change in antenna position will help some stations and kill others, since obviously the stations aren't all mounted on the same tower. This is despite the fact that all Phoenix stations will give you a strong RF signal where you are. A rotator might work for you if you don't have one already.
But multipath of any kind -- airplanes, clouds, reflections off other towers or even South Mountain itself -- or overload (especially from the dozen or so 100 kW FM stations) causing false signals within the desired channel's passband, can make stations unviewable. I found that an FM trap was mandatory when I lived 5 miles from the towers, as well as a slight adjustment of my indoor antenna for some channels.
I was not referring to my current location (directly east of S. Mountain about 8 miles down Warner Road). I have my big screen connected to a large combo outside antenna which lays on the roof of my back porch and sees S. Mountain through some rather thin pine branches. It receives virtually all the Phx metro stations except virtual 44. My computer TV is using an indoor Leaf Metro and I can switch it between the Metro and an older rabbit ears/UHF ring. Neither are amp'd. When connected to the Metro I can receive most of the stations (but not 44). The rabbit ears do a bit better but still no 44.