I had a chance to try one on before buying, it definitely is sized different than previous westerns. I'm usually a 3 or 4XL in the westerns, but based on measurements this shirt would be a 2XL for me. It would have fit exactly the same but for the armholes. Like most IH shirts the armholes are extremely high, so unless you're a skinny dude the armpits will be very tight. In order for this shirt to fit me I'd need a 4XL but then the arms are too long and the waist is too big so I'd have to do a few alterations.
It's a beautiful shirt, but the biggest issue for me is the high armholes. If you have any sort of shoulder and arm size this will be extremely tight in the armpit area so you'd have to stick with your normal size. If you're a skinny dude then you could for sure size down and it would fit very nicely.
The measurements they provide are all bang on, so you can trust the measurements like they say. However, the one measurement that I would find helpful would be the size of the armhole at the shoulder. That would allow me to determine if it would be a tight fit.