Sprite Image size for different mobile resolutions

Hello guys,

I know this issue was asked many times here so I did my HomeWork :)

So basically, if you want to develop for different platforms, you:

1- choose the one with the highest resolution. That will be your standard resolution

2- Design all your art work depending on that resolution.

3- Let Unity automatically re-scale all assets when mobile resolution differs from the chosen standard one.

I understood and was able to apply such solution. Now the question is:

Your game file size will be the same for all new and old devices right? Is there another solution which i missed that would make your game file size smaller with older devices?

Thanks for your help :)