The air is going to flow into the highest part of the suit. If you are in proper horizontal trim, that generally means along your shoulders and upper back and your lower legs and feet. If you are standing or vertical, you will get a squeeze in your lower torso. If you go head/torso down and legs up, you will feel the air start to flow into your legs and feet. You will feel more of a squeeze if you are wearing thinner layers, because thicker layers will cushion the squeeze of the trilam material more.
My guess is that one of two things are happening: 1) you think you are head down/feet up when you might not really be, and/or 2) you aren't used to having a drysuit on and don't yet have enough experience to know how it feels to dive in one. There are frequently going to be transitory moments of various amounts of slight squeeze depending on your depth, trim, undergarments, etc. A "real" squeeze is when you definitely do not have enough air in your suit and it is pressing rather uncomfortably around you and compressing your undergarments, preventing them from lofting and doing their job to keep you warm.