I know what you mean, I was afraid it would be spongy or unresponsive.
But the secret to it working is, it's quite compressed already. With the corner brackets holding the top of the step down, the foam is already small and so it squeezes and bounces back quickly.
The first panel I made, which was self-designed (to be cheap, because I couldn't afford plexi and corner brackets) was absolutely horrible. Well, my sheet metal system was flawed but also, the lack of corner brackets meant each step floated 1/4" above where it presses down. There was no way you could get it to respond on time.
You'll only get a spongy feel if you make an entire square out of the foam, because the air can't escape fast enough. There's no problem with the foam if it's well adjusted enough.