The number of black police officers is usually determined by the community / city location. In general I would think there are more black police officers in communities with majority black people, although there are still a few suburbs and areas that are the exception. I don’t have any stats to back this up though and wouldn’t want to mislead you. My interactions with police have been very limited in general - I like to think I’m law abiding and careful, but I could also just be quite lucky. I’ve only had a single encounter with a black police officer, and that fucker gave me a ticket.
I believe the percentage of black officers is proportionate with the percentage of black people in the populace (i.e. about 12-15%)
Regarding senior positions I would be surprised if there is a disproportionate amount of black officers in those roles. I do feel that the few that do exist are wheeled out as PR “puppets” as the need arises, and since most public outrage occurs due to injustice against African-Americans, it only makes sense for the police to display “one of them” whenever dust ups inevitably arise.
Listen to this if you have a moment (an hour or so), it’s one of my preferred podcasts: