Confession time.
I was wrong. I wen't back and checked the figures and the way I said it worked was totally wrong.
The score by the second placed car was discounted so that only cars finishing in a top 6 finish would score any points.
Take this example from the 1969 South African GP:
Finishing result
Stewart - Matra - 9 Points
Hill - Lotus - 6 Points
Hulme - McLaren - 4 Points
Siffert - Lotus - 3 Points
McLaren - McLaren - 2 Points
Beltiose - Matra - 1 Point.
For this result the constructors points were awarded as follows:
Matra - 9 Points
Lotus - 6 Points
McLaren - 4 Points.
So the points didn't roll downwards.
So, to review your example:
It would be as follows:
Mercedes - 25 Points
Williams - 12 Points
Red Bull - 6 Points
Ferrari - 1 Point
I'm going to take myself off and give my self a good
and wear the CTA hat of shame