How does the game determine where a Resonator is deployed?
Distance of a resonator to the portal center depends on how much close you are to the portal center.
Also if you don't select a slot, the first deploy will show your location. It starts deploying from the slot that is closest to your location and keep deploying accordingly in a clockwise fashion.
So far my observations say it's dependent on your distance from the portal. The further you are, the further the resonator will be deployed. I recommend having the portal just on the border of your action ring when deploying.