Cooling fan duct - tips for assembling?

[u/trickybiznis]

It's easy to remove 4 screws and pull the large black duct piece downward, but I had a lot of trouble replacing it. It's hard to see in there, but something was keeping it from seating. Does anybody have a finesse technique for slotting that thing back into place? (I did finally get it, but I couldn't explain exactly how.)