First, thanks for the question.
Second, the Inzer chart isn’t necessarily off but it’s a rough estimate – which isn’t perfect. It’s really close actually in my experience but we are all built quite differently.
For instance, I am 265lb but someone else at the same weight might be 5’2″ or 6’2″ which would change the interpretation of the chart juxtaposed to my build, right? Keep this in mind.
Also, doesn’t fit really doesn’t tell me much. Too big, too small? Arms of shirt too long, too short, is your torso long and it a belly shirt? Can’t get it on? Falls off of you?
What I suggest is calling Inzer 1800.222.6897 and talking to a rep. Tell them what sizes you have bought and your exact build ie long arms, thick torso etc and whats been wrong with the fit. This does make a huge difference.
Last and possibly most importantly, what is your pressing ability? If the shirt is “too small” but goes on, in reality it isn’t too small, your bench is (no offense) in many cases.
Those with a smaller relative bench will need a looser fit, and those with a bigger bench will need a tighter fit.
You should struggle to touch anything around ~80~% of your equipped max as a rule of thumb. But again, this is all depending on your ability.