How tight should an aero race jersey actually be?

It should feel compressive and slightly restrictive standing up — like a firm handshake on your entire torso. You should not be able to pinch more than 1-2cm of fabric anywhere. When you lean into your riding position, the jersey should be smooth with zero wrinkles across your back and shoulders. If it feels comfortable standing in the shop, it's too big. However, it should not restrict your breathing — if you can't take a deep breath, size up one. The jersey should feel like a second skin on the bike, not a tourniquet.