See those oval "windows" marked on the front of the dish, describing a circle near the edge? (left picture)
The instructions of the kit said "cut out". Unfortunately, the resin in that area was about 3/8th of an inch thick
which made it pretty much impossible to remove those areas.
So I decided to completely remove the inner part of the housing.
At a later point I will make a new ring with the windows cut out and insert it from inside the housing.