There is no direct scaling in the roof for party size, having more helping hands will certainly make the encounter less challenging, especially if you are well coordinated.Lastly, I'd like an official comment on how exactly the party size affect the difficulty of The Roof encounter and also how exactly luck affects the drop rate of the arties, is it the top damager's total luck when the final boss is killed ? How is the top damager is determined in this case ? Only the last boss or the 4 bosses combined ?
Each individual that winds up on the final legend's top attacker list as a result of damage taken, damage dealt, and damage healed from that legend has their own chance at getting an Artie. The luck stat of the individual can help to increase that chance.