To give a little finality to this post, here's where I ended up.
Once I removed the glove box liner again, it didn't look like I was going to gain much, but we had to try.
Here is the interference with the arm on the duct hose.
Looking at the factory duct adapter, the quick left pointing transition isn't helping things.
With as much coaxing as I could with slack that I didn't have to begin with, I gained maybe 1/2".
Half an inch still isn't going to be enough in my case, and with a little modification, the "catch leg" has been located to the bottom of the arm.
No final pictures as the touch up paint is currently drying, but the idea is there.