Full Text Searching -- is it possible to speed up query with additional where clauses?

[Joe Aliperti]

I'm trying to optimize full text queries when I have a particular subset of rows I want to search. But I've noticed that the query times do not improve. Am I doing something wrong:

e.g,

SELECT * FROM `blog_posts`
WHERE `id` IN (1,2,3)
AND MATCH (post_body) AGAINST ('+mango +smoothie' IN BOOLEAN MODE);

takes the same amount of time as:

SELECT * FROM `blog_posts`
WHERE MATCH (post_body) AGAINST ('+mango +smoothie' IN BOOLEAN MODE);

So there doesn't seem to be any time gained from drastically reducing the search pool to a small subset. Is there any way to accomplish a speedup in this case?

I'm using the InnoDB engine, id is the primary key, and there is a full text index on post_body. Thanks for any insight!