As from version 2.0 the search relevance customization is possible.
The values on the search relevance otpions page are only valid for non-fulltext searching. Fulltext lookup has a built in relevance.
The plugin defines relevance values from scale 1-10, 1 being the lowest and 10 being the highest value. You can define a relevance value for each field where the plugin looks.
The relevance is calculated based on these values with a simple formula.
The formula is:
[field 1 relevance value] x [phrase occurence in field 1] +[field 2 relevance value] x [phrase occurence in field 2] + ...
So if the title weight is 9 and the phrase "test" was found in title twice, then the title relevance is: 9 x 2 = 18
The same calculation is made for each field with the corresponding relevance value. In the and these values are summed. This sum is the result relevance.
Exact match relevance is calculated without examining each word in the phrase, only checking the exact phrase for occurences. Non-exact match relevance is the opposite, where each word is checked separately.