Document setup:

SU 850
At 50% width = 425mm,  height = 1075mm
At 25% width = 212.5mm,  height = 543.75mm

SU 1000
At 50% width = 500mm,  height = 1075mm
At 25% width = 250mm,  height = 543.75mm

SU 1200
At 50% width = 600mm,  height = 1075mm
At 25% width = 300mm,  height = 543.75mm

Don’t forget to add the equivalent of 20mm bleed on all sides at final size.