Mission scaling to lvl
Generally speaking, the team will be at the level of the team leader as they enter the arc, and will have their levels raised or dropped according to the operative levels of each mission.
However, if you were thinking you'd like to tune your custom NPCs so that they'd have fewer powers / defenses at low level and more powers / defenses at higher level, so as to better match your players, then no, you can't do that.
If the devs had a NPC profiling tool so you could make your foes scale across various level ranges, we could do it. But the devs don't even have that tool for themselves.
I've written out a fun arc for some of my friends to play on, as it has lots of inside jokes that they'll understand. I want for it to be available for all of them to play, but there's a wide range of levels their toons are at. I want it to be challenging for all of them, but don't want to kill off the lowbies just to keep the challenge for the higher lvls. So is there some way I can set the levels of the mission so it will scale with the team running the arc instead of bumping the lower lvls up to a temporary higher lvl?