First, they obviously point out that they make improvement on "COVENANT SUMMONS".
"Additionally, when performing Covenant Summons, players will now have a 5% chance to receive a Moonlight Hero. This change allows for players to have an additional chance to receive a Moonlight Hero while also maintaining their rarity when compared to regular Heroes. With the addition Moonlight Heroes, the probability of receiving a 3★ Artifact has been decreased and the overall probability of receiving a Hero is now greater than the probability of receiving an Artifact. The Moonlight Heroes that will be attainable in Covenant Summons includes all 3~5★ Moonlight Heroes. Also, when a new Moonlight Hero is introduced, they will be immediately be placed into the Covenant Summons as soon as they are released. "
This was written clearly, only when you PERFORM on COVENANT SUMMON POOL you will have 5% of summoning ML units.
They didn't jog down that they will add it on the banner or limited banner as well.