I have found this to be very true. I'm 5'10" and float between 165 and 170 lbs. Depending on the measure in their sizing chart, I am all over the place.

I have a Balance III jacket that fits great in medium. I just bought Phatom jacket and the XL fits me best. The medium and large both fit ok, but were very tight in the shoulders.

Having had some difficulty with their sizing in the past, and given that I got free shipping on the Phantom, I ordered a medium, large, and XL and returned the two that did not fit. It cost me around $8 to ship them back, so it was cheap insurance.