Guessing "modern fit" means "tight" or "body-con". Methinks those who are not stick-thin will want to order up a size.
(Aside: I ordered a 5-pack of the pastel Harvic Galaxy golf shirts for myself a couple weeks back. Should've heeded the other posters' advice and sized up. The men's 2XL did not fit my ample-bosomed self, and barely fit my XL hubby. Ended up giving them to my BIL, who wears a L [and plays a lot of golf, so he won't have to do laundry as often, LOL]).