Let me get this straight....
Instead of using one 6 inch port, you used 2 3" ports To cut down on Port lenght.
Buddy it doesnt work like that. You have the same amount of port area. You dont add the length of those vents together. If you have 2 3" vents that are 15 inches long and 12 inches tall...You have 72 Sq. Inches of vent that is 15 inches long...NOT 32 It would of been the same thing if you would of used one 6 inch vent.