[This answer is based on OP's pictures and comments about what worked in the end]
The fork has IS brake mount interface, the brake caliper is for PM (post mount) interface. An adapter to keep them together is required.
IS/PM adapters come in many variants. The main difference between them is the disc diameter difference they dictate. Just a few examples (the image taken from one of discount retailers) of visual differences between such adapters is demonstrated below. Compare No. 1 — No. 3 (No. 4 seems to be a PM/PM adapter):
An adapter marked as "+0 mm" incurs no difference in disc size. That means, if the wheel has 160 mm disc installed, it will work a fork meant to have 160 mm rotors and with +0 mm adapter. An adapter marked as "+20 mm" will require 180 mm disc to match the rest of the same setup.
Now, the trick is that the same IS/PM adapter part is asymmetric and can provide two offsets, depending on the direction it is installed.
Compare two pictures from the @MT247 question and comments.
- Adapter installed in the supposedly +20 mm position. The caliper sits too high relative the the disc, resulting in very little overlap between surfaces of brake pads and the 160 mm disc.
- The same adapter reversed and installed in the +0 mm position. The caliper allows the whole surface of brake pads to touch the 160 mm disc when braking.
Another, very confusing, culprit is that a different adapter should be installed in the back of a bike compared to what is installed in the front! That is, to work with a 160 mm rear disc and an identical caliper, a different IS/PM adapter may be required.
The key here is to carefully read the manufacturer's installation instructions and use common sense when inspecting the brake setup: brake pads and the disc must overlap over the whole area.