Valid Target (Engage Order)
With an Engage Order, an operative is a valid target if it's visible to the attacker. Being In Cover does not prevent targeting - it only provides a cover save when shot.
With an Engage Order, an operative is a valid target if it's visible to the attacker. Being In Cover does not prevent targeting - it only provides a cover save when shot.
With a Conceal Order, an operative is only a valid target if visible AND not In Cover. This is the key benefit of Conceal - being near terrain protects you from being targeted at all.
Same position, different orders. Target 1 has Engage Order - visible and In Cover means valid target with cover save. Target 2 has Conceal Order - visible but In Cover means NOT a valid target. Orders matter!
When shooting, you cannot select an enemy operative if a friendly operative is within its Control Range (1"). This is a Shoot action restriction, not part of the Valid Target definition. Other rules that check "valid target" don't include this restriction.