Surely it’s not entirely about Hg’s, but also about how your unit feels at a particular pressure. I have a 6” girth and when using a 2.25” cylinder 3 - 4 Hg is about on the limit of my comfort zone; however when using a 2” cylinder I experience the same feeling at 7 Hg, probably due to the firm packing at the sides. I’ve always worked on the basis that I want to achieve maximum expansion in the cylinder whilst ensuring the pressure feels comfortable and my unit does not incur donuts, red spots or any other form of injury. Since girth is fully packed, I’ve always assumed that I need to be stretched beyond my normal erect length whilst in the tube in order to promote length gains. I’ll experiment with lower pressures for a while when using the 2” cylinder just to see if I can still get comparable expansion levels and EQ at the reduced HG.