Today I LB my Octmon. And, like we've been discussing, raising the duplicate does indeed help.
My Octmon duplicate was in lvl 12 and, as a result, the added EXP was over 9000!!
Haha... Just joking. It was 5820 EXP. It wasn't enough for a whole lvl but... it's good!!
There's the proof, right (down) here...