constrict

They found that the eyes of people with aphantasia don’t constrict when imagining light.

But for "ha" you're constricting the air down in your throat at the vocal folds or glottis, and you can't get your tongue down your throat to create that centre blockage.

That’s certainly true for air lock, where, if you assume that gasses don’t get into pipes or that they can’t constrict the flow, you might design a pipeline that doesn’t work.