Why the Current Dimension will not become smaller, what is the relationship between Current Dimension and mipmap?

I created mipmap texture(2048 * 2048) in PhotoShop,

213934-01.jpg

import to UE4 and works well.

But the Current Dimension in the Statistics still shown(2048 * 2048) , same with the Max Dimension, I’m not sure if this is correct.

This is my texture settings:

In order to optimize the scene, how to set up to make the Current Dimension become smaller?

PS: I submitted this question because in some of other Demo files, I see some textures will be optimized, and they don’t use LOD Bias, I think this is a good idea for optimizing the scene.