If I male a request using the "tagged" parameter, the returned results are more that if I make the same request with the same tags but using the "q" parameter.

Notice that the behaviour of requests with the tagged parameter is not as described in the documentation. It works just like an AND filter, so the returned result should be exactly the same as if making a request with the q parameter and the AND filter. (See here: Tagged parameter not working as described in documentation)

Examples:

This request: https://api.stackexchange.com/2.3/search/advanced?pagesize=100&order=desc&sort=activity&accepted=True&views=50&site=english&tagged=grammar%3Bmeaning%3Bsingle-word-requests

Gives 7 results, all tagged with the 3 tags.

This request should give the same results: https://api.stackexchange.com/2.3/search/advanced?pagesize=100&order=desc&sort=activity&accepted=True&views=50&site=english&q=%5Bgrammar%5D%20and%20%5Bmeaning%5D%20and%20%5Bsingle-word-requests%5D

But it only returns 3 results.

If I make a request using the "tagged" parameter, the returned results are more that if I make the same request with the same tags but using the "q" parameter.

Notice that the behaviour of requests with the tagged parameter is not as described in the documentation. It works just like an AND filter, so the returned result should be exactly the same as if making a request with the q parameter and the AND filter. (See here: Tagged parameter not working as described in documentation)

Examples:

This request: https://api.stackexchange.com/2.3/search/advanced?pagesize=100&order=desc&sort=activity&accepted=True&views=50&site=english&tagged=grammar%3Bmeaning%3Bsingle-word-requests

Gives 7 results, all tagged with the 3 tags.

This request should give the same results: https://api.stackexchange.com/2.3/search/advanced?pagesize=100&order=desc&sort=activity&accepted=True&views=50&site=english&q=%5Bgrammar%5D%20and%20%5Bmeaning%5D%20and%20%5Bsingle-word-requests%5D

But it only returns 3 results.