If a guy has thick posterior chain (no homo) and core… he’ll look lighter than he weights.
In contrast to a guy who has small waist, not too thick of a posterior chain and core but has big show muscles (shoulders, chest,etc) and wide clavicles. I’m like this because I got tiny waist and my posterior chain and core are not developed but I got tiny waist and big chest&shoulders, and people say I look I like I weigh 20 lbs more than my actual weight.
Another example is Chris Bumstead, classic physique champ, he doesn’t weight a lot compare to other pro bbs but he’s got a small waist and wide clavicles and big chest that makes him look like he weigh 260, when he’s like 225 lbs on stage and 245-250 ish offseason I think? Some powerlifters weigh that much, but they don’t look nearly as big as Chris bumstead
This is another example, eventhough markus had thick waist, his shoulder width is out of this world, and his chest and shoulders are gargantuan. That’s why he looked way way heavier, but Ronnie Coleman is actually heavier because he’s got much thicker posterior chain.
Think of it like this as well: You will look twice as big, if you add 5 lbs muscle to your shoulders instead of 5 lbs of muscle in your core/glutes/hammies
Hope that helps