I sized down in my uniqlo OCBD.
I'm usually a large at 6'3 185 lbs but Gitman Vintage large is way to boxy and short in arms and J crew is still too wide in medium and I have 41 chest. RL custom fit in M was perfect last time I tried one. Uniqlo in M fits great, even in length.
Yep, I had to size down from my normal sizes in almost every other brand. I'm 5'11 155, 38" chest, small fits perfectly... almost too perfectly probably , since gaining a couple pounds would make them uncomfortable.