Yes, this can be true IF there are fills providing good vocals. Otherwise, you're screwed in this scenario. I did a show open where my DPAs were approx ORTF and almost directly over a vocal monitor, with an SBD feed on the other two channels providing only vocals. Without the SBD feed, there would have been way too little on the vocals. In fact, every time I've run onstage, I had to have an SBD feed to fill vocals. If you're running "stealth" mics onstage, I'm not sure how you compensate for that, since I'm assuming you're not getting a feed and may(?) be recording without permission, in which case you can't optimally place the mics...
That said, when it works, onstage is pretty amazing. I'm about to post a Soulive recording from a couple weeks ago that just flat out smokes...
the closer the better!!! personally i have been doing stealth mics on stage. the trick is getting vocals and a good mix of everything. they usually have front fill spkrs at most venues so that you get a good mix up front. up front you get the stage sound (which is best) plus the front fills. if you could get in front of a front fill, you will make one the best recordings you will ever hear. forget that sweet spot logic. that is bs. you get too much hall reverb. i got recordings that would blow your mind made up close. i am using omni's though.
You are assuming that most venues have "fills". Most of the venues I tape in don't have such things. So, closer the better doesn't always fit, but if you can pull off a fill speaker i could see it working.
You must tape in bad rooms, because the "sweet spot logic" is not bs in a good sounding room.