MyISAM spatial index is not optimal with ST_Intersects

DROP TABLE IF EXISTS t1;

CREATE TABLE t1 (

 point point NOT NULL,

 SPATIAL KEY `point` (`point`)

) ENGINE=MyISAM;

DELIMITER $$

FOR i IN 1000..5000

DO

  INSERT INTO t1 VALUES (POINT(900, 200));

END FOR;

$$

DELIMITER ;

explain SELECT * FROM t1 FORCE INDEX (point) WHERE ST_Intersects(point, GeomFromText('POLYGON((3 0, 3 3, 8 3, 8 0, 3 0))'));

+------+-------------+-------+-------+---------------+-------+---------+------+------+-------------+

| id   | select_type | table | type  | possible_keys | key   | key_len | ref  | rows | Extra       |

+------+-------------+-------+-------+---------------+-------+---------+------+------+-------------+

|    1 | SIMPLE      | t1    | range | point         | point | 34      | NULL | 4001 | Using where |

+------+-------------+-------+-------+---------------+-------+---------+------+------+-------------+

ALTER TABLE t1 ENGINE=InnoDB;

explain SELECT * FROM t1 FORCE INDEX (point) WHERE ST_Intersects(point, GeomFromText('POLYGON((3 0, 3 3, 8 3, 8 0, 3 0))'));

+------+-------------+-------+-------+---------------+-------+---------+------+------+-------------+

| id   | select_type | table | type  | possible_keys | key   | key_len | ref  | rows | Extra       |

+------+-------------+-------+-------+---------------+-------+---------+------+------+-------------+

|    1 | SIMPLE      | t1    | range | point         | point | 34      | NULL |    4 | Using where |

+------+-------------+-------+-------+---------------+-------+---------+------+------+-------------+