You have a good point when you said that towers should be near your current location. Towers have certain coverage. This mostly happen when the phone is moving or technically if you are travelling. If you are almost out of coverage on the current tower you were connected, phone will automatically connect to the next tower available. This is the reason why sometimes text messages are not sent because it was about to change tower when the phone was trying to send a text. Phone will keep on sending the text that's why we see multiple attempts to send text. Then once the phone is connected to the next tower, it will be sent successfully but that will be read as sent through the next available tower. 

If you want more explanation regarding this technical matter, we could call you and get you connected to our Technical Team instead.