Perlin noise and negative coordinates

Question

I am working with Perlin Noise and coordinates and want to know how to handle negative coordinates in order to make it not symmetric.

Example image of my Perlin noise

As you can see in the image, when perlin noise get negatives coordinates it doesn't differ from positive so you get this symmetrical noise.

The code is obviously simple:

float extension = 0.005f;
float perlinNoise = Mathf.PerlinNoise((position.x + seed) * extension, (position.y + seed) * extension);

I want to know if there is an intelligent way to get normal noise. BTW: Move away from 0,0 position or change it is not an option.

Thank you in advance.