Per Ben,
 
Ah! Tube excitation harmonics for gluing the mids!  
 
I also looked up the difference between tube mics and condenser mics (https://www.gearslutz.com/board/so-much-gear-so-little-time/152567-difference-between-tubes-plain-condencer-microphones.html).
 
I might ponder is ... how far past 'flat' might one want them 're'-doubled?  But with my sibby vocals, muddier lush may be awesome (just pondering).