I believe tren cough is cause by tren getting into the bloodstream and irritating the lungs from the inside out because tren is spicy. I use a 25g 1" needle, I aspirate while the needle is in the muscle, and I slowly inject tren into my ventrogluteal muscles. I can't recall ever getting tren cough when injecting into my ventrogluteal muscles. I've been cruising on 200mg/week test e & tren e for a few months and haven't gotten tren cough one time.
I have had severe tren cough when injecting my quads though, even when I aspirate first and inject slowly.
I don't think the ester matters.