Document setup:

RU 850
At 50% width = 425mm,  height = 1200mm
At 25% width = 212.5mm,  height = 600mm

RU 1000
At 50% width = 500mm,  height = 1200mm
At 25% width = 250mm,  height = 600mm

RU 1200
At 50% width = 600mm,  height = 1200mm
At 25% width = 300mm,  height = 600mm

Don’t forget to add the equivalent of 20mm bleed on all sides at final size. Also in document set-up allow for a non visual margin of 50mm at head and 200mm at foot at final size.