We actually still put the sail ties through the sail and around the boom with the loose foot... ever so slightly more aerodynamic that way
Yeah, you can do that too. Really no different than what we did with our fixed-foot, so it's hard to argue the point.
But I just like keeping it above the boom for a number of reasons. Foremost, I don't feel any need to go under the boom with a loose footed main. I can contain the sail every bit as well, really.
Another reason is if a reefing line parts or slips on the clutch or cleat. Under the boom, and you could tear the sail before you see it or have time to react. Above the boom, and you have a little more wiggle room before there's a problem.
Also, we sometimes sail back home fully reefed, and drop the main without shaking the reef out. Next time we're at the boat, when we go to hoist and remember the reef, we ease the reefing lines. Hopefully we get all the gaskets out too, but if you're double reefed there's more than a few of them and there's the possibility one will be missed. So again, more wiggle room for a human error.
With an ace crew, you might not worry about any of these issues. I sail with my family, and there's a lot of distractions, so anything I can do to give me a second chance...