Pretty well known Adonis is about 5'9. Guys like Bika and Karpency are around 5'11-6'0 at the tallest and they dwarfed him by 2-3 inches at least. Look at when Stevenson fought Bellew who is 6'2, the top of his head came up to Bellew's eyes. Kovalev looks like he is a legit 6'0.
In situations like this you can generally assume the guy who seems taller than he is listed is simply listed correctly whereas most people are overlisted. I notice a lot of continental European fighters tend to be listed accurately which can make British or US fighters look a bit silly. Wlad for example really is only 6'5" and change, like he says, but because everyone else is overlisted he comes out looking 6'7".