I'm 5'10" and around 230, typical beer gut normally XL in tops and L bottoms. Have large SEAK jacket as it was cheap on ebay and all my other FL tops in XL are overly loose on me. It fits perfect, still allows for layering up to my FL unpronounceable although it is a little tight but not bad. But with a chama/halstead and vest which i'll wear mostly its perfect. I don't care for the overly loose fit on my other FL xl tops but was able to shrink my chama and springer vest in the dryer for better fit. If you like a looser fit and want to layer up more than might want to try xl.
I am 6’ 225#. I bought a large and it fits fine without nothing more than a sweatshirt underneath. If I ever layer a puffy underneath it gets pretty snug in the shoulder, arms and upper back area. Without anything underneath it fits perfect. But I still wish I would’ve jumped up a size to an extra large for when I do need to layer.