Was hoping to get some sizing advice. Was ready to pull the trigger on a size Small (i'm 5'9" 145 lbs) but noticed that AJ who is similarly sized to me is a size Medium. I am a size small on all IH shirt across the board however i recently sold my Whipcord Work Jacket (IHJ-61) because it was difficult to wear any thick sweaters comfortably underneath. I assume there is no liner in this which means it will wear slightly larger? I still think I am a small but any encouragement is appreciated.

Are people generally sizing up one on these? i am generally a size S however I also wear a size M on the heavy duty t-shirts.