Pixel size and effective permeability

I am trying to calculate the effective permeability for a 3D porous media with the size of 3000x3000x3000 pixels and 10x10x10 micro^3. I resized (not crop) my model since my 3D model is very large to make the computations faster and generated a smaller version (200x200x200 pixels). I am wondering how should I assign the new configuration for the resized model? Do I need to use the same size of 10x10x10 micro^3 for the resized model or I need to change it accordingly? Indeed, as you know, the effective permeability is very sensitive for the pixel size and it changes once the sizes change.

Thanks for your help.