I have a Lantana built in 2012. Have same problem. The flex duct in the attic is R4 which is the minimum. R8 would be nice. A lot of lost thru ducts. They also put the "return air" grill too close to the "supply' grill in all the bedrooms. You can try adjusting the supply as far away from return as possible. I am having the "foil" energy shield installed in the attic next week, hoping this will help. (cost $1900 for Lantana). I am also looking into putting insulation over the ducts or blowing more insulation in the attic and trying to cover the ducts. You may want to walk thru the attic and check the insulation, I found several spots where it was low and they came back under warranty and added. What ever bedroom has the "tray ceiling" has R13 batts not R30.
