An ESL diaphragm will move as a flat planar piston with all bending taking place at the edge – but only above the low-end resonance. Near or below fundamental resonance, the stiffness or stretch of the plastic dominates over the air load and you get a drum head shape (probably a catenary curve). In the vicinity of resonance, you’ll probably see a blending of planar with catenary – talk about tough math! High above resonance, where most of the action is anyway, the air load dominates over the plastic stretch, except at the constrained edges. Here is an opportunity for further research. Since so much bending is taking place across such small dimensions near the edge, are there better ways to build a trampoline-like suspension? Is the stretching producing any chaotic behavior (tiny crinkling noises) at -80, -90 or -100dB? John Atkinson commented on this chaotic behavior after measuring ESLs but didn't understand the source of it. Maybe I’m making a mountain out of a mole hill; I don’t know. By the way, cones generate all kinds of chaotic noises (scrapes, cone bending noises, turbulence, etc), and probably a lot more than ESLs.