Here is a close up of the actual bracket fitted this one is an 8V4 919 291
before
You can see I have had to drill 2 holes in the holder and make 2 slots at the connector end to make it fit the bumper mountings, the 'face of the bracket and the rear of the bumper were then 'flatted' with coarse emery paper until the sensor was perfectly flush with the front of the grill, If I were to do it again I would use my newly acquired plastic' 'melting' skills learned when changing the drivers arm rest for power folding mirrors, and melt the 2 round locating lugs like rivets after gluing to hold it even tighter, as that's what I now realise they look as though they were intended for.
Note this holder has a '2' on it. the holders are moulded at slightly different angles depending where they are fitted on the bumper, i.e. on a corner (angled) or in the centre (flat)
An angled bracket
I will have a 'rummage' and look if I saved any more info when I was trying to understand this.
If you do paint any sensors here is the spec and how I achieved it, I used the sensor cutter to cut 2 holes in a small piece of plastic and then placed the sensors behind it with no seal this leaves enough space for the paint to fully cover the corners but not the base of the sensor body, again the paint I used was Audi Titan granit metallic mixed by BSS with satin lacquer. PDC system operates perfectly.
The pins and washers are the ones off the top of my slam panel which were starting to look untidy, they now match the slam panel and are almost invisible.
hope this helps.