Parameter initialization in a genetic algorithm
In my opinion you should make the range as large as possible (to a reasonable extent) for the first random initialization. 

The genetic algorithm will converge to the appropriate range eventually, but giving it a narrow range could result in a sub-optimal solution because the algorithm doesn't have any way to reach a better solution. The only downside of a large range is that it might take a bit longer (more generations) to converge.

So I would suggest you keep a completely random initialization of the values, for instance in the range [-10,10].