SQL & PL/SQL

i am using 11g

CREATE TABLE EX_COMPRESS
( id NUMBER, xml_document XMLType
) XMLTYPE COLUMN xml_document STORE AS SECUREFILE BINARY XML(COMPRESS HIGH)




CREATE TABLE EX_NOCOMPRESS
( id NUMBER, xml_document XMLType
) XMLTYPE COLUMN xml_document STORE AS SECUREFILE BINARY XML(NOCOMPRESS)




SELECT segment_name, bytes
FROM user_segments
WHERE segment_name IN('EX_COMPRESS','EX_NOCOMPRESS')



BEGIN
FOR i IN 1 .. 1000 LOOP

INSERT INTO EX_COMPRESS
VALUES (I,
XMLType(bfilename('MYDIRECT', 'purchaseorder.xml'),
nls_charset_id('AL32UTF9')));


INSERT INTO EX_NOCOMPRESS
VALUES (I,
XMLType(bfilename('MYDIRECT', 'purchaseorder.xml'),
nls_charset_id('AL32UTF9')));
END LOOP;
COMMIT;


END;



SELECT segment_name, bytes
FROM user_segments
WHERE segment_name IN('EX_COMPRESS','EX_NOCOMPRESS')


o/p is

segment_name BYTES
........................
EX_COMPRESS 917504
EX_NOCOMPRESS 720896

in the o/p for compress no bytes for compress is more comapre to nocompress why it happend?

normally for compress no bytes less compare to nocompress