Raymond, just curious why you would put two heavy favorites in a parlay? If a 2 team parlay should pay say 13:5, anything less that you receive is an edge you give back to the house. Personally, I think the house already has the edge, so why give them more? It's sorta like doubling down into the 10 at BJ table. In your 2 teamer, you are getting back 7.5:5, if BOTH teams win. I think in this case you are better off with just 2 straight wagers.
I try and look for dogs to parlay, at least two of them. Sometimes I will look for two solid dogs in early games and parlay with a favorite in late game. This can help set up a nice hedge play if you hit the first 2.