Correctness of the greedy algorithm
If I am right, the configuration below leads to a 7 blocks greedy solution (on the left). By symmetry, all four directions.



But there is an 8 blocks solution (on the right).



The problem with a greedy approach is that "consuming" a block can destroy two other possible blocks, and have a negative impact.

Repeating the search in different directions will not fix this, as it is possible to build symmetric patterns that result to the same behavior in all directions.