I have a couple of pics I went searching for which show the lens at an angle , which may make the OE construction a bit clearer.
The lights I am using are VW Golf Mk3 ( 1992-1999) front bumper indicators & side repeater lamps, the lens have an ideal slight curve and the pattern in the lens to look just right. The bulb holder ideally is for a BAY9s bulb and the holder comes from a VW passat or Audi TT , then at the moment the side repeater body mounts to the headlamp shell.