I’m not sure but mine is also 8, and I just copied from @flyingsolow which is quoted in your post pic.
Here is my edited table:
Mana troop on ofense significant reduce tiles, and with Costume, the gap is like this IMO:
Level 1, Level 5, Level 11, Level 17, Level 23.
So, every gap (leveled) is significant (based on which heroes we have).
Short-plan focus on 1x mana Troop level 17, other mana troop on Lvl 11, and some level 5 in each color. (Depend on heroes we want to plan stack).