Strange results of Indexing services

Question

Currently I am working on Indexing services to search document from Windows server. I am using following Query to search "F-0350"

Query

Select rank,Filename,Size,HitCount from Scope() where CONTAINS(Contents, 'ISABOUT('F-0350' WEIGHT(1.0))')

Query Result:

 Rank          FileName         Size    HitCount
    572   sf ob-0350.prod.xml   2521    4
    572   sf g-0350.prod.xml    1199    4
    572   sf qa-0350.prod.xml   1864    4
    572   sf f-0350.prod.xml    1551    4
    362   sf ob-0353.prod.xml   2469    4

I am expecting 4th record on top but its not coming.