A comprehensive model is developed from ab-initio calculations to understand the effects of co-implanted fluorine (F) on boron (B) and phosphorus (P) under sub-amorphizing and amorphizing conditions. The depth of the amorphous-crystalline interface and the implant depth of F are the key parameters to understand the interactions. Under sub-amorphizing conditions, B and P diffusion are enhanced, in contrast to amorphized regions where the model predicts retarded diffusion. This analysis predicts the F effect on B and P to be entirely due to interactions of F with point-defects.