Twisted Domain difficulty & monster level question

So I killed Xesht 2 times, first without any breach nodes (monster level 80), then with one +1 difficulty node (monster level 81) on Atlas Breach points. Now I'm trying to use the Breachstone with 2 of these +1 difficulty nodes to get another book of skill, but the Realmgate still says "Monster level: 81". Does it still mean that it is a higher "difficulty" although the monster "level" is the same? Shouldn't it be monster level 82 with +2 difficulty nodes?

I have the same issue