I read a great article about an engineer called Tom Elmhirst who worked on some Amy Winehouse tracks on her latest album.
He mentioned her voice having 'hard' frequencies present, which he EQ'd out at pretty exact points, using a very narrow Q.
As a singer myself, this interested me because I sometimes find myself thinking that my voice has these 'hard' frequencies which might be a little hard to take for the listener. By the way, I am not comparing myself to Amy Winehouse, who has one of the most amazing voices I have ever heard!
Then I was on a flight listening to my REM on my iPod. If you listen to Everybody Hurts, their most famous track, you hear what might be described as 'hard' frequencies in Stipe's voice.
I would take the term 'hard', to mean piercing and therefore a little hard (no pun intended!) on the listener.
So maybe some surgical EQ is what's needed to take out the harshness and warm things up by taking the cold out?
Also from personal experience I can say that the distance from the mic has to be dynamic rather than constant. I would definitely agree that an approximate distance from the mic is what is needed to start with, but you can't say 6", or 12" or 10" etc because it depends on the singer.
Does the singer have a powerful voice? No? Then closer is better, but not too close obviously. If the singer has a voice like Little Richard (!), then you'd better keep that dude further away! Or maybe use a dynamic mic rather than a condenser...? Mick Jagger uses a dynamic mic, so does Bono... SM58 as far as I know.
Anyway I'm rambling now, but I hope I've helped a little.
Lastly, what you've got on the Logic channel strip, does it really matter? What I mean is, because they're inserts and don't actually effect the signal as opposed to hardware... am I right?
Oh one more tip, always send the vocalist some reverb, it helps a lot!