tp550i, yes the offset helps, but it's real thight.
I just took some mesurement tonight, and adding tips to the muffler really increases the space required.
Now i'm just debating if i go for it or not. hmmmm
advice on a exhaust system for A 2012 528i
sorry can't help, as i dont have one, but from Realoem,
I see the 528 uses the same 70mm clamp i used on my 550i.
So you could get a custom exhaust made locally, clamp on style. if you ever want to return to stock. and not have issues of rewelding the system.