Is Match Against suitable for string similarity check in MySQL?

Question

I have a field (tags_ids) that contains tags id of products in comma-separated format. To find similar products, I wrote a query like below :

select * , MATCH (tags_ids) AGAINST('1000,1001,1002,1004' IN NATURAL LANGUAGE MODE) as score from product ORDER BY score DESC

And the result :

array (size=7)
  0 => 
    array (size=2)
      'tags_ids' => string '1000,1001,1002,1004' (length=19)
      'score' => float 0.35009866952896
  1 => 
    array (size=2)
      'tags_ids' => string '1004' (length=4)
      'score' => float 0.15835624933243
  2 => 
    array (size=2)
      'tags_ids' => string '1002' (length=4)
      'score' => float 0.15835624933243
  3 => 
    array (size=2)
      'tags_ids' => string '1000,1001' (length=9)
      'score' => float 0.033386167138815
  4 => 
    array (size=2)
      'tags_ids' => string '1001,1006' (length=9)
      'score' => float 0.023994617164135
  5 => 
    array (size=2)
      'tags_ids' => string '1000' (length=4)
      'score' => float 0.0093915509060025
  6 => 
    array (size=2)
      'tags_ids' => string '1003,1000' (length=9)
      'score' => float 0.0093915509060025

But I want element number 3 ('1000,1001') be in second priority (rather than '1004'). The string '1000,1001' isn't more like the '1000,1001,1002,1004' than '1002' !?

There is mistake in my query or match-against is not suitable for such application? Is there a better solution?

Note : I replaced comma with space but result was exactly the same