I've heard this phrase in a podcast called "Tigerbelly" One of the podcasters said that "his girlfriend could be sitting 3 seats over and still smell his feet"
I tough it might mean "on the other side of " as in this def
On the other side of: a village over the border. (source freedictionary.com)
I though he meant she was 3 seats away but on the other side of the aisle, as on a plane or bus.