Prodigal Son said:
The main thing is to do whatever feels most comfortable to you when doing EE, and you can vary your position as you go through EE. For example I tend to stand for three-stage pipe-breathing, sit for BaHa (when I do it), and lay on the floor for PotS.
The "ha" sound on exhalation is 'protracted out for the full count', and will arise naturally if your throat is slightly constricted on the out-breath, and for its duration.
I agree with Prodigal Son, do whatever feels most comfortable to you. I like to do the three stage breathing sat on the floor but with some back support, so either leaning against the wall or the sofa, or the head of the bed. Ba-ha lying down and also the meditation lying down.
To be absolutely clear on the "ha" sound (as I misunderstood this to begin with), it’s just the sound of the air passing through the wind pipe not a literal "ha" produced by the vocal chords. Laura says "ha" on the audio as a reminder for us to pipe-breathe, but we don’t literally say "ha", it’s more of a soft sound as you would get when breathing onto a pane of glass to steam it up.
The sound is controlled and made equally over the full measure of the count, so try not to let all the air escape at once when first exhaling so you don’t end up with a big "ha" on count 1 and then nothing towards count 9. Working on that consistency over the full measure will help develop control of the diaphragm too.