You're not doing anything wrong, the tactics available unfortunately do not support moving patrol areas. It's sort of a bummer. It's been a problem ever since "Against All Odds" from 688I, yet we still don't have it...
There may be light at the end of the tunnel, though. If LW's helo dipping mod has any success, you could use waypoints to get the helo to dip at certain intervals, or perhaps even use triggers and scripts to get the helo to dip at a certain range in front of the ships.
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