I've seen a couple of techniques that can be used to lessen the coughing, its slower more gentle inhalation, I have emphysema and find if I try to inhale everything at once that'll make me cough, not first time around moreso the 2nd go of the device, rushing to get it into my lungs, we all do it

. I know we are all different too, it might be heat related or the
THC tickle which you think its your chest. Many things can make you cough, having the right cooling accessories, the right bong if using one, sometimes your mouth can be too near the heat source if having sensitive lungs.