Under what condition do the reaction proceed with sole removal of oxygen in contrast with the product also ending up with chlorine substituent?

[![Deoxygenation of pyridine N-oxides with PCl3](https://i.stack.imgur.com/xTQsZ.png)](https://i.stack.imgur.com/xTQsZ.png)

I'm familiar with both reaction mechanism, but can't seem to figure out when will a certain pyridine end up with or without chlorine. I guess one factor would be electron richness of the ring system, chlorine being deactivating subsituent ends up only on the electron rich pyridines.