QT is best really especially if you have other nems, you can actually pass a bacterial infection.
As for forcing close proximity, we do not advise doing that, you could actually harm your clowns if they have not adapted to nems sting cells.
I do turn flow down until they attach, but once they do I put back to normal right away, and I only would diffuse light if I thought they came from much weaker light than mine, otherwise they may move seeking different flow and light, and i usually place them where I'm pretty sure it's going to be about right, so far I'm on a pretty good long roll of my nems staying put this way.