I don't think its actually the coughing that makes you higher, I just think that the reason you cough is when you take a really big hit. People don't cough when they take a small hit so they don't get as high. But when you take a big hit you cough and get really high so it seems like if you don't cough you don't get as high and if you do cough you get higher but its actually just the size of the hit. The coughing doesn't cause the high, the big hit does, but the big hit also causes the coughing.