Comment by amalcon

Those few degrees matter if your knees are already brushing the back of the seat in front of you. It matters how tall you are, how much of that is in your legs, how big your feet are (the more you need to bend your knees, the higher they will be), and it also varies depending on seat design and layout.

For others like me, one trick is to at most minimally use the under seat storage: small handbags only. No backpacks, briefcases, or anything else big enough to hold a laptop. Then, you can put your feet in that space. This lowers my knees by 1-2 inches depending on the plane, which really matters. It's the only thing that helps significantly, aside from paying for premium economy. Doesn't help with the claustrophobia, but there's not much to be done about that.

The other things I've tried (that don't reliably work) are leaning forward from the seat back (to pull my knees back) and slouching slightly (so that the inevitable recline compresses the seat back into my knees rather than bashing them). The former saves my knees, but sacrifices my back. The latter kind of helps during the flight, but walking will still hurt the next day.