When you query the SharePoint Search Service the number of rows returned defaults to 100 but can be increased as required.
Note that when you specify a value above the maximum RowLimit the query will only return the default value of 100 items !
ServerContext ctx = ServerContext.Default;
FullTextSqlQuery query = new FullTextSqlQuery(ctx);
query.QueryText = BuildQuery();
query.ResultTypes = ResultType.RelevantResults;
query.RowLimit = 1000;
ResultTable resultTable = query.Execute()[ResultType.RelevantResults];
After some trial and error I found the maximum value for the RowLimit to be 917728059.
query.RowLimit = 917728059;
So don't go around setting the RowLimit to int.MaxValue like I did because this only returns 100 items...