A Quick story:
A guy north of me (15 miles) was using a Maco 104 on a 50' tower - when the Pacific stations were coming in strong, I was having to relay to him what they were saying. He just could not hear a lot of them like I could.
Now, the next summer, he install a 5 element on the same tower and through the next winter he was able to hear all the stations that I was hearing - never had to relay for him again!
So the only thing that changed was; he went to a bigger antenna.