The Fosta 410cz-3 uses even elastic compression around the ankle and a built-in rib for lateral reinforcement. The tension of the side Velcro closure determines how firmly the rib presses against the ankle, so the right setting is the point where the brace feels stable without creating pressure points.
As a practical rule, put the support on over clean, dry skin or a thin sock and pull the Velcro strap to a snug position. You should be able to slide one finger between the fabric and your skin, but not comfortably wiggle it around. The ankle should feel held, not squeezed. When you move your foot up and down or from side to side, the brace should stay in place and the Velcro should not dig in.
If you feel tingling, numbness, a pins-and-needles sensation, or see the toes changing colour, loosen the strap or remove the support. These are signs that the compression may be too strong. Swelling can also change during the day, so re-check the fit after activity or in the evening; one closure position is not necessarily right for the whole day.
If you are using the brace after an injury, or if you have a condition that affects circulation or skin sensation, ask a specialist before use.