At the end of the day nitrous is simply extra oxygen content so like a forced induction engine it should be mapped for correct AFR and detonation.

When used to achieve a small percentage power increase the cooling effect of nitrous will actually reduce the detonation/pinking limit and as such when increasing power by 10 - 15% with nitrous it usually does not require any ignition retardation. Like wise there can be a small reduction in egt's again meaning that AFR's can remain similar to the non nitrous setup.

However when running in excess of 25% power increase with nitrous the car MUST be mapped correctly for both fueling and ignition requirements. I'm not prepared to give figures though as thats part of my trade that you pay for!!