New answers tagged hydraulic-disc-brake
If your fork is a post mount, and your rotor is 160mm, you will not need additional adapters or spacers to fit a Shimano brake. The image from the manual you posted is correct.
There are some assumptions in your question that make it next to impossible to answer. Braking is not a static operation. The friction of any wheel is directly proportional to the weight currently being supported by that wheel. As you brake the effective "weight" moves from the both wheels to almost entirely on the front wheel. The harder you brake ...
Don't worry about equal torque. The front wheel will do as much as ninety percent of the work on a maximum stop. You will learn to modulate the rear to prevent lock-up. Equal pressure will be fine for normal stops.
Assuming the same force applied by the cylinder and the same materials, with the same pad size, the larger rotor will have a larger "lever arm" and be more "effective", in proportion to the diameter.
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