silverstripe-fulltextsearch/docs/en/04_advanced_configuration/44_boosting.md

Boosting/Weighting

Results aren't all created equal. Matches in some fields are more important than others; for example, a page Title might be considered more relevant to the user than terms in the Content field.

To account for this, a "weighting" (or "boosting") factor can be applied to each searched field. The default value is 1.0, anything below that will decrease the relevance, anything above increases it.

To adjust the relative values, pass them in as the third argument to your addSearchTerm() call:

use My\Namespace\Index\MyIndex;
use SilverStripe\FullTextSearch\Search\Queries\SearchQuery;
use Page;

$query = SearchQuery::create()
    ->addSearchTerm(
        'fire',
        null, // don't limit the classes to search
        [
            Page::class . '_Title' => 1.5,
            Page::class . '_Content' => 1.0,
            Page::class . '_SecretParagraph' => 0.1,
        ]
    );
$results = singleton(MyIndex::class)->search($query);

This will ensure that Title is given higher priority for matches than Content, which is well above SecretParagraph.