This speaker is a real wonder. The cone, compilance and magnet are identical to those speakers described as 165mm (at the rear in DS4), but there are no mounting points around the cone beause compilance is glued with distance. This reduces the overall diameter of the speaker. The visible collar (removable) fills the gaps in the upholstery for the 165mm speaker size. Therefore, with the appropriate distance, you can easily use a custom 165 speaker (as you wrote)
I would suggest to by from dealership rear mount for the rear speaker and place it in front.
I think they are the same or will require not much of adaptation.
Okay You’re right but the dealership should be able to provide spacers for car with front Focal system which has 165mm front door speakers.
If the speaker is not glued/integrated to the basket like in the 130mm (default - no Focal speakers), it would be ideal.
Whole assemby looked like this if I remember correctly but important thing is that the speaker is held by screws and it is not integrated with the basket.