Why is my device with "normal" screen dividied by Android studio as "small" screen device?

I have that problem:

i have two layout folders layout-small and layout

When i change rendering device on preview when editing layout to Nexus S (It have "normal" screen) Android studio will open the layout-small and let me edit small screen layout which is displayed on Nexus S.

Same issues with other "normal" screen devices

thank you for your answers.