Black Knight is an average hero and needs a level 23 mana troop (13% mana bonus). Since you gave him the mana node, he’ll need a level 17 troop (11% mana bonus) to charge in 9 tiles. He’ll still charge in 10 tiles even with a mana troop level 11.
It’s probably the same with Hel and Telluria, only the level 17 mana troop will help them charge in 9 tiles.
Here’s a very useful thread about mana generation made by @ThePirateKing:
