Directional influences question

[RECON51]

Just set up 2 identical base stations 10 miles apart with no ground topography to speak of between them. Both with half waves about 50 ft up. Both have stryker 955 radios with sub 1.5 swr.
1st transmission the afternoon we set up the northern base station in Havana, signal was coming in loud and clear in Tallahassee, but the signal from Tally was weak in Havana. Next morning we tried again. We were talking clear as cellphones both directions on AM and SSB. 5 hrs later, north to south was loud and clear but south to north was again pretty grainy sounding. There was a lot of skip from up north like Ohio, Pennsylvania etc. at the times when the local signals were crappy. Is this just a normal weather / time of day thing? And why would the signal only get crappy on one end? Both of the locations are pretty rural. Please feel free to be long winded, I'm here to learn.

[Tim]

In brief, someone 10 miles away from each other may receive and even transmit a different signal strength, propagation is like that, the same can be said for ground wave to a certain extent.