Small for sure

This is quite timely for me. I am 5'9" with 31-32" inseams, very proportional regarding torso and leg length. I took a small for a test ride and it felt good. I am working with a very good Retul fitter and he seems to think the small is good. Perhaps its a preconceived notion, but I keep feeling like I should be on a medium. On the small I am looking at, the seat post is in the rearward position, the stem has the 2 spacers and the arm pads have all the spacers there. I will qualify that the bike has not had a final fit, but was set up "close" to my current bike, Orbea Ora. Part of my issue is the use of all the spacers and the rearward seatpost, does that indicate that it is too small or just the way it needs to be for a good fit. I will mention that I am moving up to iron distance and am looking for comfort above aero.

Thanks for the help.