Bad news, Barry: mana troops need to be at level 23 to move average heroes down to 9 tiles. Level 17 is to take Slow heroes from 12 to 11 tiles, which is less helpful. Reference:
To answer your question, though: Other than prioritizing a red and yellow mana troop at L11, I first brought crit troops to L18, then shifting back to working on the mana troops. Is that optimal? I’m not sure. L18 adds one percentage point to the crit chance; arguably stopping at L15 (which is, I think, when the attack stat goes to 17%) may be better.