Using a Koster-Slater one band-one-side approximation, the relationship between the pressure behavior of nitrogen bound excitons and the band structure is investigated in GaP and GaAs1-xPx. An analytical expression is found to be a good approximation for the pressure coefficient of the deep impurity state. The pressure coefficients of N and NNi bound exciton states are calculated in GaP and GaAs0.17P0.83. A tentative new assignment which agrees with experiments in both ordering of levels and pressure coefficients is given for nitrogen pair configurations.