I don't completely agree here. But you point about no compression in a straight tube VS a curved tube is mostly right. But some of my comments had to do with the length of the rear triangle and where the load is WRT your butt. The further rearward of your butt the load enters the rear triangle the less displacement you feel.

On another fitting aspect the amount of seat set back will effect the weight you feel on your hands. (Somewhat independent of your reach length). When you butt (I love that word) is well positioned above (and behind by the "right" amount) your feet you can support your upper body with your core and not only your arms/upper body. The way my boss shows this is to ask riders to go from the hoods to letting go and sitting upright. With poor core usage one tends to push back with their hands as they sit up. With good positioning that employs your core the sitting up motion is fluid and needs no help from your arms. Additionally when dropping back down to the bars the motion is not one of "falling" and "catching. It took some wrapping of my mind around this idea but I've seen it during fitting sessions many times. Andy.