Mine are similar, more or less:
but have a single flat support piece in the middle. That support fits into a rectangular sleeve that runs down the center of the back of the seat, supported at the top and bottom, with a couple of long, spring steel pieces that hold it in place where-ever set:
I can remove the headrest entirely by inserting a small screwdriver into a small slot at the top and then pulling the headrest right out.
They're also adjustable fore and aft as you wish - especially good for when I'm older with curvature of the spine from bicycle riding for 60 years: