There will never be two IDENTICAL antennas with IDENTICAL "angles of attack"
Now if you have a vertical with a very low angle of attack (lets say 90deg for this discusion) and you are talking to a local station within 60 miles and they have a higher angle of attack (say 30 deg) but there are running the same power output and there antenna is " Identical"to yours in respect to gain. They will here you better than you will here them.
The reason being is that there signal has most of the RF density broadcasting upward toward the sky, versus yours where the majority of the RF density is being transmitted along the earths surface.
This same principal however does not work for DX. Once RF enters the atmosphere, the D and E regions as well as the others will "refract" the signal at verying degrees. So if the majority of your signal hits the atmosphere at lets say a 45 degree angel, it may exit at a 70 degree angle. Theres also other phenomenon to consider, like coastal ducting, Aura, Sparadic E, meteor reflection, and so on.
As a general rule of thumb The lower the angel of radiation, The further DX you will work.
And the Higher the angel of radiation, the closer dx you will work.
This also becomes null when considering what frequency you are refrencing. The higher the frequency the less effect the atmosphere will have.
I hope this isnt too confusing