So my insurance co-pay is different for generic, preferred brand, and non-preferred brand of medications. I know what the difference between generic and brand name is, but does anyone know what most insurance companies use to determine a preferred brand vs. a non-preferred brand?

On my insurance, Latuda is a non-preferred brand, so my copay is $70 (which I know is nothing to what it costs without insurance). I did however find on the manufacturer website for Latuda a savings card to reduce your copay by up to $75 (you pay a minimum of $25), so I plan to use it for as long as I can. The card is only good until the end of June though, so after then I will be back to paying the full insurance copay, unless by then it is a "preferred" brand...then I'd only pay $40...I just don't know what criteria insurance companies use to separate "preferred" from "non-preferred" brands. Does anyone have any clue here?