There is nothing inherently wrong with your sizing. I appreciate looking at the description where it says "model has a 39" chest and is wearing a medium" This is perfect and helps me understand the fit better.

What I would like to see is the more obtuse sizing like some of the Hugo Boss shirts have an international 40 size and the sizing guide recommends to me International 40, but I don't know what that means. Is it 40 around the neck? Chest? Some brands will say size 42 and I assume its neck size, and some from the same brand will say Medium or give out a chest size. Some explanation or guide on these more uncommon size charts need some keys. International 40 for a shirt means nothing if I dont know what it means.

For example - I am a 16" neck or 42cm neck for dress shirts. But I click on a shirt from X brand and it goes from International 38 to 50. The size guide says it recommends International 50. Another brand will say International 40 and I dont buy it because I am worried I will be purchasing something in the wrong size and have to go through a returns process.

I hope this helps - Im not complaining, just letting you know why I sometimes I dont buy some items at times.