Those must be, at least partially, ghosted tiles? Four ghosted tiles will charge a fast mana hero… 3 ghosted + 1 non-ghosted should be enough for GM, maybe even 2 + 2 with your mana boosting troop, not really sure there. But surely not 4 non-ghosted tiles…? If that’s true, then my information is incorrect.
But if we’re talking ghosted tiles, then a slow mana hero will only need 6 of those of course.
One thing I did apparently get wrong, a very fast mana hero takes 6.5 non-ghosted mana tiles to charge. I thought I’ve seen 7 mentioned at some point… must be old age 
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