optimal 4 x 4

def board_maker(rows, cols):
    w = rows * cols

    def n2b(n):
        s = f'{bin(n)[2:]:>0{w}}'
        s = s.replace('0', 'M').replace('1', 'B')
        return [list(x) for x in zip(*[iter(s)] * rows)]

    def calc(n):
        return calculate_score(n2b(n))

    return n2b, calc

def iter_neighbors(board, x,y):
    n = len(board)
    m = max(map(len, board))

    for dx in (-1,0,1):
        for dy in (-1, 0, 1):
            if dx == dy == 0: continue
            if dy+y < 0 or dy+y >= n or dx+x < 0 or dx+x >= m: continue
            yield board[dy+y][dx+x]

n2b, calc = board_maker(4, 4)

n = max(range(2 ** 16), key=calc)

display(n2b(n))