Location of custom node in ribbon

Hi all, 

I have recently started creating my own custom components. I can set the tab and the "sub-tab" for the component, but I am wondering how the program determines the sub-sections within that sub-tab. For example, under Sets/List, how do all the components with lists end up at the top? In the custom nodes, I have created, it seems that their placement in these sub-sections are random, but I am not sure this is the case. Can I set this location if I am creating custom nodes through Visual Studio Visual C#? 

Thanks!