Disposal of Interest while retaining control- Technical Article example

Hello,

I am hoping someone can please help clarify. I am studying the technical article for Business combination and there is an example where the company disposed of 5% interest while retaining control. Because NCI was measured at FV the solution just adds Net assets at disposal date and good will then multiplies it to get the increase in NCI (basically CA of interest disposed) I studied using BPP and this is not the approach I was thought, Goodwill doesn’t come to play since control was retained. Well I guess is make sense that they want to apportion the portion of goodwill the group lost…anyway, is this the understanding everyone else has, should I disregard BPP?

Thank you!!