Hi, calculate stock EOI and keep EOI close to stock when you make a remap.
That will be more than good for your case.
If you have ECU with duration in degrees than it is very simple to calculate EOI,
if you have in microseconds than you have to calculate over rail pressure map and duration map and soi map...
There is very nice thread from ALEX, he made a program for calculating EOI, you may find it useful for you:
eoi-builder-t1441?hilit=affect%20on%20soicheers