I'm not sure if this was always like that but currently (in 0.15) if inserters try to put items straight they always do put items on North/East side despite of their orientation
I will attach screenshot describing this.
Imo inserters should put items say on far side and to the right of their pointer so when you turn it 180 degrees it will start offloading to another side of the belt.
Basing on this intuitive logic I designed the marathon green circuit build