Draw imaginary lines from any point of the attacker's base to every part of the target's base that is facing the attacker. Anything that at least one of these lines crosses is Intervening.
The operative's player draws imaginary straight lines 1mm in diameter from any point of its base to every facing part of the intended target's base. Anything at least one of these lines cross is intervening.
When an attacker has a Vantage Point (elevated position), the same Intervening rules apply. Draw lines from the attacker's base to the target's base - terrain that crosses these lines is Intervening.
If there's a difference in height between the operatives (e.g. one of them is on Vantage terrain), targeting lines should be drawn in a three-dimensional manner.
When shooting at an elevated target, the same Intervening rules apply. Draw lines from the attacker's base to the target's base - terrain that crosses these lines is Intervening.
Only terrain can intervene for Cover and Obscured purposes. Other operatives do not count as Intervening, even if the targeting lines pass through them.
Anything at least one of these lines cross is intervening.
While operatives don't count as Intervening, if an operative's physical model completely blocks visibility from head to target, the target is not visible. This is rare in practice.