I'm totally new to this - I am still in the "gathering stuff" stage and haven't even made my first recipe yet, so if I'm off base don't kill me..
But from what I understand maltodextrin doesn't really do anything for the sweetness in soda, it's just a 'heading' agent. I know it is used as a fluffy carrier medium for sucralose (Splenda) in order to make it a "cup for cup" replacement..
If the flavors aren't combining on the palate, I would think that they were not boiled together for a long enough period. Maybe also try using a finer milled sugar?