The rule of 3 somewhat overrides it if your local groups go with that, but the rule you are looking for is in the sidebar on page 114 of the Codex. It means in matched play no more than four Court models in a Detachment with an Archon, and none otherwise.
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From a midnight sky, there is a searing flash, a boom, a brief moment of destruction, and then it is gone.
Kabal of Lightning Strikes - Project Log
Drukhari damage output analysis