85 Bronco Defroster Q

[85 Bronco]

Hello, I am new here. My 85 Bronco has terrible defrosters. I took apart the lower end of the unit, and the "floor" flapper is closed, but even with the unit set on "defrost", I get much more heat out of the vents than at the windshield.
I also noticed that the plastic ductwork to the defrosters is wide and very narrow.
Is this a common problem with bronco's of this era?

Thanks for any help,
Karl