This comment @Giles:
We do use the same pattern. But different weaves and even different dyes make each fabric behave totally differently. Celebrate it. We are not the only company that has variations in what look like the same thing, but we are one of the only few (maybe the only one), that publish individual measurements, not a general all tag size X measure Y.
is one of the reasons I am hooked on IH. Studying size charts before making a purchase is half the fun and being able to get clothes that fit just right rather than 4 generic sizes is what more companies should be doing.