I am not sure if a generic method to avoid this situation wouldn't backfire for a number of other users. If we limit the size to the smaller screen, I could imagine users of embedded systems running into the opposite problem: If you have a very small display and a decent-sized one, would you really want to limit everything to the size of that small one, in many cases making YaST windows unusable? Before we start working on a dramatic change, please check if you can configure what Qt considers its "primary screen". It might be a setting in your KDE desktop somewhere.