Well, with 4 boxes to form a group, the max is 9. If the boxes are set up like this:
____B
____B
BBB_B
___B_
___B_
___B_
If they push the lowermost row of three up one spot, all boxes'll have to disappear. Same when they push the horizontal row one more to the right.
In the same way, the max for a group formed with at least 3 is 6.
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