Getting different results while using bool query vs bool query with function score query

Elastic Stack Elasticsearch
1

I am trying to add a custom boost to the different should clauses in the bool query, but I am getting different number of results when I use the bool query with 2 should clauses containing 2 simple query string query vs a bool query with 2 should clauses with 2 function score query encapsulating the same simple query string queries.
The following query returns me 2 results for my data set:
{
"query" : {
"filtered" : {
"query" : {
"bool" : {
"should" : [ {
"simple_query_string" : {
"query" : "128",
"fields" : [ "content.name_enu.simple" ]
}
}, {
"simple_query_string" : {
"query" : "128",
"fields" : [ "content.name_enu.simple_with_numeric" ]
}
} ]
}
},
"filter" : {
"bool" : {
"must" : [ {
"term" : {
"securityInfo.securityType" : "open"
}
}, {
"bool" : {
"must" : [ {
"term" : {
"sourceId.sourceSystem" : "jmeter_007971_numeric"
}
}, {
"term" : {
"sourceId.type" : "file"
}
} ]
}
} ],
"_cache" : true
}
}
}
},
"fields" : [ "elementId", "sourceId.id", "sourceId.type", "sourceId.sourceSystem", "sourceVersion", "content.name_enu" ]
}

Where as if I use the following query I get 5 results, same simple query strings but with function scores:
{
"query" : {
"filtered" : {
"query" : {
"bool" : {
"should" : [ {
"function_score" : {
"query" : {
"simple_query_string" : {
"query" : "128",
"fields" : [ "content.name_enu.simple" ]
}
},
"boost_factor" : 1.5
}
}, {
"function_score" : {
"query" : {
"simple_query_string" : {
"query" : "128",
"fields" : [ "content.name_enu.simple_with_numeric" ]
}
},
"boost_factor" : 2.5
}
} ]
}
},
"filter" : {
"bool" : {
"must" : [ {
"term" : {
"securityInfo.securityType" : "open"
}
}, {
"bool" : {
"must" : [ {
"term" : {
"sourceId.sourceSystem" : "jmeter_007971_numeric"
}
}, {
"term" : {
"sourceId.type" : "file"
}
} ]
}
} ],
"_cache" : true
}
}
}
},
"fields" : [ "elementId", "sourceId.id", "sourceId.type", "sourceId.sourceSystem", "sourceVersion", "content.name_enu" ]
}

From my understanding of how the should clause works I was expecting both the queries to return 5 results but I am not able to understand why the 1st query returns me 2 results for my data set. The "content.name_enu.simple" uses a simple analyzer, whereas simple_with_numeric uses whitespace tokenizer and lowercase filter