fminsearch. How does the first variable works?

[IC,SurfaceValues,exitFlag]=fminsearch(@integratePlanetODEs,IC,[],extPar);

This is a line of a code and IC could supposedly vary from -inf to +inf but I changed the scale so it varies from 0 to 1. I'm the one who choose the first value for IC and then the program will vary IC so the min value will be searched. But IC vary just a little bit. Example IC = 0.5 and then its variation is only 0.49999 to 0.56999 that's so small. I need IC to vary more because I have a value attached to IC. So whenever IC vary this other value varies too so I have different outcomes and it's supposed to get the smallest one. So how does IC vary? that's my question. what are the rules that rules its variation?

Thank you all